I agree with retrochic. A face to face meeting is going to be the best way to reach agreement with your clients. One would have thought that the clients would be aware of the fact that you had not invoiced them. If they are of any size, they would have (or at least, should have) included a provision for your invoices in their accounts. You must also consider the Income Tax/ Corporation Tax implications. You will have understated - and the cllients, if they have not provided for your fees - overstated profits. Presuming that you are registered for VAT (and if you can afford not to notice £50K turnover, it is likely that you are) you are invoicing some time after the tax point. If your clients cannot afford to pay your invoices in one hit, you need to set up a payment schedule, preferably by standing order/direct debit. Legally, you are entitled to the money but if you can come to an amicable agreement rather than having to go legal it would be better. If they are ongoing clients you are more likely to resolve the problem without dispute. Finally, schedule your time so that you ALWAYS raise invoices on a certain day of the month, whether your clients need them or not. I am glad I am not your accountant! Good luck with your negotiations.