The invoice, the delivery note and the dates clipped together, which is most of what a payment dispute is decided on.
The first thing to know is that an unpaid invoice is a process problem before it is a people problem. Most late payments trace to a purchase order nobody requested, an invoice sent to the person who commissioned you rather than the person who pays, or a payment run that happens monthly and just missed you. The remedy is boring: send the right paper to the right desk, then follow a written reminder sequence on fixed dates.
For the fuller version of that routine, the guide Informdebtor lays out chasing an unpaid invoice as a sequence of documented steps: the evidence file, the reminder ladder, the point where you identify what is actually being disputed, and the escalation options by jurisdiction. It is written for businesses, which is what you are the moment you invoice someone.
What makes an invoice collectable?
An invoice is collectable when the story it tells is complete. That means the agreement behind it in writing, even if the writing is an email thread; the work delivered and accepted, with a date; the invoice itself carrying the agreed figure, a payment term and where to pay; and a record of every message after it. Each piece answers one excuse a late payer might reach for.
Two habits do most of the work. Confirm the sum and the payment term in writing before you start, so the invoice arrives as a formality rather than a surprise. And send the invoice the day the work is accepted, because the payment term runs from receipt, and every week you delay sending is a week added to when the money lands.
When do reminders become escalation?
A reminder ladder has a simple shape: a polite nudge a few days after the due date, a firmer note a week later restating the amount and the date, then a final notice that names the next step. The moment a reminder stops being the tool is when the client stops disputing the process and starts disputing the work. At that point you are no longer chasing a payment, you are arguing about acceptance, and the evidence file matters more than the tone of the email.
In the UK, late commercial payment has a statutory framework behind it: interest and fixed compensation can be claimed on overdue business debts, and the rules are set out on the government's page on late commercial payments. Knowing that page exists changes the final reminder more than any wording does.
Paper first, then sequence, then escalate:
- Agreement, delivery and invoice all in writing before you are owed anything.
- Reminders on fixed dates, getting firmer, each one recorded.
- When the dispute moves from process to the work itself, the evidence file does the talking.
The limit: a routine cannot make a bad client pay on time, it can only make your position orderly and your escalation credible. For sums under a few hundred pounds, the time cost of escalation sometimes exceeds the invoice, and writing it off is a legitimate business decision rather than a defeat. The calculation is easier when the paper is already in order.
The same keep-everything-in-writing habit protects you earlier in the chain: reading the contracts nobody explained covers the document you sign before the first invoice exists.