try this...
"We reserve the right to charge for late payments in accordance with The Late Payments of Commercial Debts (Interest) Act 1998, and subsequent legislation"
This allows for interest as previously stated (8% above Bank of England base rate for commercial, or 8% for consumer, per day from date invoice fell due to the date of the notice)
It also allows you to charge compensation charges as follows:
invoice valued to £999 = £40
£1,000 - £9,999 = £70
£10,000 + = £100
But the statement on it's own will suffice - as these are statutory rights for all businesses.
HTH...
OR - you could follow Sean's quicker link which spells it out too! (Oh to be young(er) again!) Well done Sean!