The Concentration Risk in Your Ledger: When a Major Customer Stops Paying

Late payment rarely arrives without warning. It usually begins with a missed promise, a query raised late in the month, or a finance team that suddenly needs duplicate invoices. For a small business, the danger is not only the sum outstanding. It is concentration risk: one customer accounts for a large share of turnover, and that customer's cash-flow problem becomes your own.

As of November 2026, many SMEs are still managing tighter credit conditions and longer payment cycles. A key account that was once reliable can become a source of acute strain. The response should be measured, documented and commercially sensible. It should also begin before the relationship reaches breaking point.

Read the early signals

Payment distress seldom appears as a formal announcement. It shows up in patterns. An invoice that is usually paid within terms is suddenly queried. A routine approval is escalated to a director who is difficult to reach. The customer asks for extended terms, then misses the revised date. Staff who normally handle accounts payable leave, or the finance contact changes without explanation.

Other signals may sit outside the ledger. Trade credit insurers withdraw cover. A credit reference report shows county court judgments or late filings at Companies House. Suppliers in the same sector begin to talk. None of these facts proves insolvency, but together they justify a review of exposure.

The practical step is to calculate how much of your turnover, and how much of your working capital, depends on that customer. If the answer is uncomfortable, treat the account as a risk to be managed rather than a relationship to be preserved at all costs.

Revisit the contract before the relationship hardens

A dispute is easier to handle when the paperwork is clear. Check the signed terms, the order in which they were incorporated, and whether they were varied by later emails or purchase orders. Look closely at payment terms, interest clauses, suspension rights, termination provisions and any right to set off sums owed.

Under the Late Payment of Commercial Debts (Interest) Act 1998, business-to-business debts may attract statutory interest and fixed compensation in many cases. A well-drafted contract can reinforce those rights, but it cannot rescue a business that has failed to identify the correct contracting party. Confirm whether you are dealing with a limited company, a partnership or a sole trader, and keep that evidence.

If the customer is a large organisation, check whether its own purchase order terms purport to override your terms. The battle of the forms is rarely entertaining and often expensive. Take advice before assuming that your standard terms prevailed.

Retention of title: useful, not magic

Retention of title clauses can be valuable where goods have been supplied and remain identifiable. A well-drafted clause may allow you to recover unpaid stock, provided it was incorporated into the contract before delivery and is enforceable in the circumstances.

It is not a universal remedy. Goods may have been incorporated into other products, mixed with other stock or sold on. A clause that seeks to claim proceeds of sale or a wider share of the customer's assets may be challenged. Enforcement also carries practical and reputational risk. Recovery should be planned, not improvised.

If retention of title matters to your business, review the clause now rather than after a default. Ensure it is brought to the customer's attention, refers to the correct goods and is supported by delivery records that identify what was supplied.

Personal guarantees and other security

Where a customer is a small company, a personal guarantee may provide an additional route to recovery. But guarantees are not self-enforcing. Check that the guarantee was properly signed, that consideration existed, and that the guarantor understood the commitment. Independent legal advice for the guarantor is prudent and may reduce the risk of a later challenge.

Other forms of security, such as a charge or a bond, are less common in ordinary trading relationships but may be appropriate for large exposures. If you already hold security, confirm that it has been perfected and that you understand the priority position.

Build the evidence file early

Formal recovery depends on proof. Assemble the purchase order, signed terms, delivery notes, invoices, statements of account and correspondence. Keep a chronology of promises, admissions and disputes. If a customer accepts that a sum is due but cannot pay, record that acceptance in writing.

Avoid relying on memory or a single account manager's inbox. Export relevant emails, keep call notes and identify who said what and when. If the customer disputes part of an invoice, isolate the undisputed element and press for payment of that sum.

Escalate deliberately

Polite chasing has its place, but it should not continue indefinitely. Move from routine reminders to a director-level conversation. Ask for a payment proposal and confirm it in writing. Make clear that interest and recovery costs may follow default, but keep the tone professional.

If payment still does not arrive, a letter before claim is usually the appropriate next step. It should identify the debt, set out the basis of the claim and give a reasonable deadline. Follow any relevant pre-action protocol and take advice on the correct forum and procedure.

If insolvency looms

Check Companies House and the Gazette for insolvency notices. If the customer enters administration, a moratorium may restrict recovery action. If it enters liquidation, you may need to submit a proof of debt to the liquidator. Do not keep supplying on credit merely to preserve the relationship; if you continue, consider cash terms, staged payments or a deposit.

Protect the rest of the ledger

The best time to manage concentration risk is before it crystallises. Set credit limits, monitor them and diversify where possible. Consider credit insurance or staged payments for large orders. Review terms annually and make sure your team knows how to escalate a late payment.

A key customer can be a valuable asset. It can also be a single point of failure. The sensible approach is neither panic nor passivity, but a documented, contractual and commercially proportionate response.