You did the job or supplied the goods at their request - there is a contract and they should pay within a reasonable time.So far as your profit and overheads are concerned it is none of their business - do you think they would give you the same information? These sort of questions get asked as a stalling tactic - I would go straight to court and sue them. If it s less than ��5000 (I think) you can do-it-yourself via the small claims procedure. For more info http://www.hmcourts-service.gov.uk/infoa��For next time I advise that you put a time limit on your invoice Terms strictly 21 days or similar. If yoyu are supplying goods then also stipulatre that they remain your property until they are paid for. That s difficult to enforce especially if they have sold them on but it s worth trying.
Check invoices you receive from others.Notice the riders included informing you of your payment options and time limit for payment expectations.Work a statement like that into your invoices to deter clients from stalling in the future.The current client is probably financially strapped and hoping you will forget the matter. You may need to consult someone for legal advice. Even though you are the business person in the matter the Better Business Bureau or Chamber of Commerce (or equivalent in UK) may be able to advise you.