Serious answer
If you're a freelancer in the UK, some companies either don't know or don't want you to know that you can charge/bill them interest for late payments.
Clients who pay late must by law pay compensation and penalty interest.
The Late Payment of Commercial Debt (Interest) Act (1988) was amended in 2002 to include fixed penalties in addition to interest. For debt of less than £1000 the penalty is £40, rising to £70 for debts up to £9,999.99 and £100 above that. Interest is payable at 8 per cent over Bank of England base rate. The penalties and interest now apply to all businesses regardless of size.
The payment clock starts ticking when you deliver the work, or on the day when your client has notice of the amount they owe you, whichever is the later. The client then has 30 days to pay - unless the freelance and the client agree on a reasonable alternative period. Clients must not pressure freelances or attempt to impose unreasonable payment terms.
Be clear when you invoice for work that "payment is due within 30 days".
The UK government suggests this form of words on invoices:
We understand and will exercise our statutory right to interest and compensation for debt recovery costs under the late payment legislation if we are not paid according to agreed credit terms.
but the law applies whether or not you mention it on an invoice.
Copies of the official guide should be available from the government and industry website www.payontime.co.uk