Entirely my fault but just discovered I've been calculating my companies flat rate vat wrong for the past 2.5 years - all the time I've been vat registered. I've therefore underpaid HMRC to the tune of Ł6.5k.
Fortunately it doesn't look like I'll be fined or have to pay interest as the sum is less than Ł10k, but I'm annoyed all the same. Grrr!!!!