Unpaid Invoice After Part-Completed Work
- William Slivinsky
- 2 days ago
- 6 min read
An unpaid invoice after part-completed work can be difficult for any business owner, contractor or self-employed service provider. You may have spent time, supplied materials, booked labour, attended the customer’s property and carried out a significant part of the job. The customer may then refuse to pay because they say the work was not finished, was defective, with one due skill and care or did not achieve what they expected.
In these situations, the question is not only whether you sent an invoice. The real issue is whether the right to payment has legally arisen. That may depend on the contract, the stage reached, the evidence, and whether the work was complete or substantially complete.
Unpaid Invoice After Part-Completed Work: why completion matters
Where a business agrees to carry out work for a fixed price, the starting point is the contract. What exactly did the customer agree to buy? Was it one complete result, or was the work divided into separate stages?
This matters because the law treats an “entire” contract differently from a divisible contract. An entire contract is one where payment is linked to completing the whole job. A divisible contract is one where separate parts or stages can be valued and paid for separately.
The Court of Appeal discussed this issue in Cleveland Bridge UK Ltd v Multiplex Constructions (UK) Ltd. The judgment referred to the older case of Sumpter v Hedges, where the court stated that where there is a contract to do work for a lump sum, “the contract price cannot be recovered until the work is completed.”
The mechanism above is the entire contract rule, derived from Sumpter v Hedges, under which a contractor engaged for a lump sum cannot recover the contract price unless the agreed work has been completed, subject to limited exceptions such as substantial performance or a true basis for quantum meruit.
That does not mean every unfinished job leaves the supplier with no remedy. But it does mean that a business should be careful before assuming that “some work done” automatically equals “invoice payable”.
The authority also refers to the distinction between divisible and entire contracts. If the contract is divisible, a party may recover payment for completed divisible parts. But if the contract is entire, a party in breach may generally obtain no recompense if the innocent party ends the contract before it has been “substantially or wholly performed.”
In plain English, the key questions are:
Did you complete the job?
If not, did you substantially complete it?
Was the unfinished part minor, or did it go to the heart of the agreement?
Was the price broken into stages or milestones?
Did the customer freely accept the benefit of the part-completed work?
Were materials supplied and retained by the customer?
For unpaid invoice claims, this is important because the court may look beyond the invoice itself. The invoice is evidence of what you claim. It is not always proof that the legal right to payment has arisen.
If the customer is refusing to pay, you should also consider whether their reason is a genuine legal defence or simply a refusal to pay. You can read more here: Unpaid invoice recovery: what counts as a real defence?
If the work was substantially complete, a business may still have a good claim, although the customer may argue for a deduction for defects or unfinished items. If the work was only partly complete, the claim may depend on whether the contract allowed stage payments, whether the customer accepted part performance, or whether identifiable materials were supplied and retained.
This point is separate from a normal Consumer Rights Act 2015 complaint about poor workmanship or defects. Here, the issue is the older common law doctrine about payment under an entire contract. If the work was substantially complete, a business may still have a claim for payment, although the customer may argue for a deduction for genuine defects or unfinished items. If the work was only partly complete, the claim may depend on whether the contract allowed stage payments, whether the customer freely accepted the part performance, or whether identifiable materials were supplied, retained and used.
Practical risk for business owners and self-employed providers
The risk for business owners and self-employed providers is that poor contract wording can turn a simple unpaid invoice into a legal argument about completion.
For example, if your quote says “kitchen installation — £5,000” with no stages, the customer may argue that payment is only due when the whole installation is complete.
If your quote separates design, materials, delivery, installation and finishing works, you may have a stronger argument that some parts were separately completed and payable.
Evidence also matters. Keep the quote, messages, photographs, completion notes, delivery records, snagging lists and any customer approvals. If the customer used the work, kept the materials, delayed access, or prevented you from returning to finish, that may be important.
As a business, you should understand the difference between a genuine poor-workmanship complaint and a customer simply being unhappy with the final outcome. For B2C work, a customer may raise a dispute under the Consumer Rights Act 2015. Section 49 requires the trader to carry out the service with reasonable care and skill. It does not automatically mean the trader guarantees every result the customer hoped for. Some outcomes may depend on customer choices, the condition of the property or site, access, materials supplied, third-party work, maintenance, or later use. So, if a customer refuses to pay, the key question is not simply whether they dislike the result. The key question is whether the trader actually failed to use reasonable care and skill, whether that failure caused the alleged problem, and whether any deduction from the invoice is fair and proportionate.
You should also be careful about escalation. Some unpaid invoice pressure tactics may be inappropriate if there is a genuine dispute about the debt. For example, where a debt is disputed on substantial grounds, aggressive insolvency pressure can create risk. You can read more here: Unpaid invoices and winding-up petitions: when pressure becomes risky
Free validation of your unpaid invoice
If you are dealing with an Unpaid Invoice After Part-Completed Work, it is worth checking the strength of the claim before sending a final demand or starting court action.
You can use our free unpaid invoice validation page here:
This can help you identify whether your invoice is likely to be recoverable, whether the customer may have a defence, and what evidence you should prepare before taking the next step.
How we can help
If a customer is refusing to pay because they say the work was unfinished, defective or not worth the invoice, you need to check the legal position before escalating. We can review the quote, invoice, messages and evidence, then help you identify whether you have a full invoice claim, a reduced claim, or a risk that the contract was not sufficiently completed.
A short legal review can often help you send a stronger payment letter and avoid wasting time on a weak claim.
FAQs
Can I claim an unpaid invoice if I did not finish the job?
It depends on the contract and the facts. If the contract required one complete result for one price, you may need to show completion or substantial completion. If the contract was divided into stages, you may be able to claim for stages that were completed.
What does substantial completion mean?
In this context, it means the work was completed in substance, even if minor items remained. The authority refers to whether an entire contract was “substantially or wholly performed”. If the remaining work is significant, the customer may argue that payment is not due or should be reduced.
What if the customer stopped me from finishing?
That can change the position. If the customer prevented completion, refused access, cancelled without justification, or kept the benefit of your work, you may have arguments for payment or damages. The evidence will be important, especially messages, appointments, photographs and offers to return.
Can I charge for materials even if the work was not finished?
Possibly. The authority discusses a limited distinction between incomplete work and materials left with and used by the customer. A claim for materials may be stronger where the customer retained and used identifiable materials, but this does not automatically mean you can charge for all unfinished labour.
Is sending an invoice enough to prove the debt?
No. An invoice helps show what you are claiming, but the court will still consider whether the right to payment has arisen under the contract. The quote, agreed scope, completion evidence, customer communications and any defects or snagging issues may all matter.
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