A procedural mistake in a bill of costs does not automatically make the bill invalid.
That is the central message from Duffy v Birmingham City Council [2026] EWCA Civ 146, a Court of Appeal decision arising from a Housing Disrepair claim.
The claimant served a signed bill of costs and Notice of Commencement after the underlying claim settled. One of the certification boxes on the bill had not been completed. Birmingham City Council did not serve Points of Dispute within the required period and the claimant obtained a Default Costs Certificate.
The Council later argued that the missing certification meant the bill was a nullity and that detailed assessment proceedings had never validly commenced.
The Court of Appeal rejected that argument.
It held that the omission made the bill defective, but did not automatically invalidate it. The solicitor’s signature itself carried an implicit certification that the bill complied with the indemnity principle.
For claimant firms, the judgment is helpful. However, it should not be misunderstood as permission to serve incomplete or inaccurate bills. The practical lesson is more balanced: technical errors do not necessarily destroy detailed assessment proceedings, but accurate Housing Disrepair costs drafting and proper certification remain essential.
What Happened in Duffy v Birmingham City Council?
The underlying proceedings concerned Housing Disrepair.
The claim concluded by consent order in October 2022. Birmingham City Council was required to pay the claimant’s costs, with those costs to be assessed if they could not be agreed. The claimant subsequently served:
- a Notice of Commencement;
- a signed bill of costs;
- and the documents required to commence detailed assessment.
The bill totalled £26,809.60.
Under CPR 47.9, the paying party generally has 21 days after service of the Notice of Commencement to serve Points of Dispute. The Council did not serve Points of Dispute within that period. The claimant therefore obtained a Default Costs Certificate in January 2023.
The Council applied to have that certificate set aside. Its arguments developed during the proceedings, but the point that reached the Court of Appeal was whether the bill had been incapable of commencing detailed assessment because an express certification box had not been ticked.
What Was Missing From the Bill?
The bill had been signed by the claimant’s solicitor.
However, the solicitor had not completed the separate certification confirming that the costs claimed did not exceed the costs the receiving party was liable to pay. That certification concerns the indemnity principle.
In broad terms, the indemnity principle prevents a receiving party from recovering more from the paying party than the receiving party is liable to pay its own legal representatives.
The Council argued that the express certification was mandatory under Practice Direction 47. Its case was that failure to complete it meant:
- the bill was invalid;
- detailed assessment proceedings had not commenced;
- the 21-day period for Points of Dispute had not validly started;
- and the claimant had not been entitled to obtain a Default Costs Certificate.
That argument would have treated the bill as a nullity from the outset.
What Did the Court of Appeal Decide?
The Court of Appeal dismissed the Council’s appeal.
The bill was defective because the express certification had not been completed, but the defect did not automatically make the bill invalid. The Court’s reasoning rested on several important points.
A solicitor’s signature carries an implicit certification
The bill had been signed by the claimant’s solicitor.
The Court treated that signature as carrying an implicit confirmation that the bill complied with the indemnity principle. Solicitors are officers of the court. Signing a bill is not an empty administrative act. It carries professional responsibility for the accuracy and legitimacy of the bill. The missing box therefore did not mean that there was no certification at all.
Mandatory wording does not make every breach fatal
Practice Direction 47 imposes mandatory requirements for bills of costs. However, the Court distinguished between:
- a failure to comply with a requirement;
- and a failure so fundamental that the document is automatically invalid.
Not every procedural breach produces nullity. The court must consider the nature and effect of the defect rather than assuming that all non-compliance has the same consequence.
CPR 3.10 applies to procedural errors
CPR 3.10 provides that an error of procedure does not automatically invalidate a step taken in proceedings unless the court orders otherwise. The court may also make an order to remedy the error. The missing certification was therefore capable of being treated as a procedural defect rather than something that erased the detailed assessment proceedings altogether.
The paying party should engage with the process
The Council had received the bill and Notice of Commencement but did not serve Points of Dispute within the required period. The Court’s approach makes clear that a paying party should not ignore a served bill because it believes there is a defect. The safer course is to:
- serve Points of Dispute within time;
- identify the alleged defect;
- reserve the relevant procedural arguments;
- and seek an appropriate direction or remedy.
A paying party that does nothing risks a Default Costs Certificate.
Did the Default Costs Certificate Remain in Place?
The Court of Appeal held that the bill had validly commenced detailed assessment proceedings despite the defect. The claimant had therefore been entitled to request a Default Costs Certificate after the Council failed to serve Points of Dispute. The Council could not have the certificate set aside as of right merely by arguing that the bill was a nullity.
However, the judgment did not remove the separate discretionary power to set aside a Default Costs Certificate under CPR 47.12(2). That distinction is important. Duffy confirms that the missing certification did not automatically invalidate the process. It does not mean that a Default Costs Certificate can never be set aside where there is a proper discretionary basis.
Why Is Duffy Important for Housing Disrepair Costs?
Although the legal point applies beyond Housing Disrepair, the factual background makes the decision particularly relevant to claimant HDR firms. Housing Disrepair costs disputes commonly involve:
- bills served after a consent order or settlement;
- standard-basis costs;
- surveyor disbursements;
- disputed hourly rates;
- proportionality arguments;
- Notices of Commencement;
- late or absent Points of Dispute;
- applications for Default Costs Certificates;
- technical challenges to bill format or service.
Duffy confirms that courts will distinguish between a procedural defect and a document that is truly incapable of commencing detailed assessment. It also reinforces the importance of complying with CPR Part 47 deadlines — a theme we explore in our guide to Housing Disrepair costs in 2026.
Does Duffy Mean Bill Certification No Longer Matters?
No. This would be the wrong conclusion.
The express certification remained a mandatory requirement. The bill in Duffy was defective. The claimant succeeded because the particular omission did not render the signed bill a nullity. That does not mean every defect will receive the same treatment. A defective bill may still lead to:
- an objection in Points of Dispute;
- an application for directions;
- an order requiring correction;
- a costs sanction;
- delay;
- an adjournment;
- loss of credibility;
- or, in a sufficiently serious case, strike-out or another procedural consequence.
Duffy protects receiving parties from an excessively technical nullity argument. It does not remove the obligation to prepare bills accurately.
Which Bill Defects Could Still Cause Problems?
The judgment concerned a specific omission from a bill that had otherwise been signed and served. Other defects may be more serious. Potential problems include:
- failure to sign the bill;
- incorrect receiving or paying party details;
- failure to identify the costs order;
- inaccurate fee earner rates;
- missing or incorrect VAT treatment;
- failure to provide required documents;
- incorrect service;
- an inaccurate statement of costs liability;
- failure to reflect the retainer;
- mathematical errors;
- misleading certification;
- defective phase coding in an electronic bill;
- material non-compliance with Practice Direction 47.
The effect of any defect will depend on its nature, the prejudice caused and the order the court considers appropriate. There is no safe rule that every bill error is curable without consequence.
What Does Duffy Mean for Receiving Parties?
For receiving parties, Duffy provides useful protection against attempts to turn a limited procedural mistake into a complete defeat of the assessment process. The practical lessons are:
Check the bill before service
Do not rely on Duffy as a safety net. Before service, check:
- the solicitor’s signature;
- the indemnity principle certification;
- VAT certification;
- the costs order;
- fee earner information;
- rates;
- calculations;
- disbursements;
- service details;
- required supporting documents.
Keep evidence of service
The history of the case also demonstrates why service evidence matters. Retain:
- the covering email or letter;
- delivery confirmation;
- evidence of any agreement to accept email service;
- the version of the bill served;
- the N252;
- attachments;
- and the service date calculation.
Monitor the Points of Dispute deadline
Once detailed assessment has validly commenced, diarise the expiry of the 21-day period. If no Points of Dispute are served, consider promptly whether to request a Default Costs Certificate.
Do not assume silence means settlement
A paying party may miss the deadline and then apply to set aside the certificate. The file should therefore remain organised and capable of defending any later application.
What Does Duffy Mean for Paying Parties?
The judgment also sends a clear warning to paying parties. If a bill appears defective, ignoring it is dangerous. A paying party should usually:
- calculate the Points of Dispute deadline;
- serve Points of Dispute within time;
- identify the alleged defect clearly;
- explain the remedy sought;
- consider whether an application is genuinely proportionate;
- avoid assuming that non-compliance automatically means nullity.
A technical challenge does not stop the CPR 47 timetable simply because the paying party believes the bill is defective.
Why Points of Dispute Remain Crucial
Duffy strengthens the practical importance of Points of Dispute. If the paying party objects to:
- certification;
- the indemnity principle;
- hourly rates;
- disbursements;
- proportionality;
- duplicated work;
- counsel’s fees;
- surveyor fees;
- or bill format,
those objections should ordinarily be raised through the detailed assessment process. The paying party cannot safely sit back, miss the deadline and expect a technical argument to restore its position automatically. For claimant firms, this makes accurate deadline management particularly important — see the common Housing Disrepair Points of Dispute we regularly answer.
The Proportionality Lesson From the Appeal
The case also contains a wider lesson about proportionality in costs litigation.
The original bill was approximately £26,800. The Council’s own costs for the Court of Appeal stage were reported to exceed £45,000, before considering earlier and adverse costs. That does not determine the legal issue, but it illustrates the danger of allowing a technical costs argument to become more expensive than the underlying dispute. Both receiving and paying parties should ask:
- What is the value of the bill?
- What is the realistic reduction in dispute?
- What will the application cost?
- Can the issue be addressed through Points of Dispute?
- Is an amendment or clarification sufficient?
- Is the litigation strategy proportionate?
Costs disputes should still be approached commercially.
Practical Checklist Before Serving a Housing Disrepair Bill
Before serving an HDR bill, check the following:
- Is the correct costs order or settlement agreement identified?
- Is the bill signed?
- Has the indemnity principle certification been completed?
- Has the VAT certification been completed correctly?
- Are the receiving and paying parties correctly named?
- Are fee earners correctly identified and graded?
- Are the hourly rates accurate?
- Are surveyor and other disbursements supported?
- Is the chronology accurate?
- Is the bill consistent with the underlying file?
- Are the calculations correct?
- Is Precedent S required?
- Is the Notice of Commencement complete?
- Are all required documents enclosed?
- Is service valid?
- Has the Points of Dispute deadline been diarised?
- Is evidence of service retained?
- Is the file ready for a possible technical challenge?
Duffy may prevent one type of defect from being fatal, but avoiding the defect remains the better outcome.
What Should Claimant Firms Do if a Defect Is Discovered After Service?
The answer depends on the defect. Do not automatically withdraw and re-serve the bill without considering the consequences. Instead:
- identify exactly what is wrong;
- determine whether the defect is material;
- check whether the paying party has raised it;
- consider whether clarification or correction is appropriate;
- assess whether re-service would affect deadlines;
- consider CPR 3.10;
- preserve the evidence showing what was served;
- take costs advice before making a procedural concession.
A minor error may be capable of correction. A substantive error affecting the amount claimed, the indemnity principle or the paying party’s ability to understand the bill may require a different approach.
Does Duffy Apply Only to Housing Disrepair Claims?
No.
The underlying dispute was a Housing Disrepair claim, but the Court of Appeal’s reasoning concerns detailed assessment procedure generally. The decision may be relevant to bills arising from:
- clinical negligence;
- personal injury;
- industrial disease;
- MoD NIHL;
- commercial litigation;
- professional negligence;
- property litigation;
- other standard-basis costs claims.
However, the case is particularly valuable for HDR firms because it arose from the same bill, N252, Points of Dispute and Default Costs Certificate process they regularly encounter. Where damages settle pre-issue but costs remain unpaid, it also sits alongside CPR 46.14 costs-only proceedings.
The Main Takeaways From Duffy
The decision can be reduced to six practical points:
- A defect does not automatically make a bill a nullity.
- A solicitor’s signature may carry an implicit indemnity-principle certification.
- CPR 3.10 can prevent a procedural error from automatically invalidating a step.
- Paying parties should raise defects through Points of Dispute.
- Missing the Points of Dispute deadline remains dangerous.
- Duffy does not excuse poor or careless bill preparation.
How DMD Costs Can Help
DMD Costs works with claimant solicitor firms on Housing Disrepair costs from bill preparation through to settlement. We can assist with:
- Housing Disrepair bills of costs;
- Precedent S electronic bills;
- N252 and Notice of Commencement;
- bill certification checks;
- Points of Dispute;
- Replies;
- Default Costs Certificate issues;
- proportionality arguments;
- surveyor fee disputes;
- hourly rate challenges;
- detailed assessment preparation;
- costs negotiation.
If a bill has been challenged on a technical ground, send us your Housing Disrepair costs file — the bill, Notice of Commencement, proof of service, Points of Dispute or application, costs order and relevant correspondence. We will review the costs position and help identify the most practical route forward.