quick question re charging interest on late payers

[007helen]

I've seen interest mentioned re late payment at the bottom of invoices before, usually at 4 percent above the base rate of whatever Bank. Silly question but does the bank rate quoted have to be that of the bank the business banks with! Do most businesses include this term re interest, how do you word it?
Thanks in adavce

[Alpha]

The interest rate is that decided by the Bank of England and is the one which gets reported every month so there is no problem in working out what it is.