I've already sent last quarters VAT return online. I have now realised I have overstated an invoice from the EC by aroung £3000 ish. It makes no difference to the amount owed to HMRC, it's purely the EC purchases figure that will differ, is it worth mentioning this to the VAT people?
If the amount of VAT is unchanged, then you don't need to do anything; although you could fire an email through their web site. If the net invoice is unchanged, what about the related VAT (acquisition tax)?