Late Payment Interest Charges

[MagicLlama]

DB has been consistently fleeced by a supplier over a number of years in the business he plays at running runs.

They are charging him interest on his outstanding balance some months and not others, but the rate is 2% per month. I understood that interest was statutory rates unless a contract was signed. As far as I know he has signed no contract with them saying that contractual interest rates apply, but does the fact that he has essentially been paying 2% over the years he has traded with them does that mean there is a contract in force, or can I query the interest rate?

Ta

Sorry just to add.

It does say (now although it hasn't any other year) on the bottom of the invoice that 2.5% interest will be charged on late payment, which I assume means that they can do it.

Additionally he has just contra'd a load of stuff with them (they've essentially brought some of his goods) and they are not offsetting that against previous years debts, but instead saying that's allocated again current year purchases?

Seems a bit crap to me, as I've always worked on a pay off oldest debt first basis, and would assume contras worked the same.