I have recently registered and have to backdate vat 2 years. I have sent all my clients VAT only invoices for what they owe, as they have paid the original invoices already. When this money comes in, it will be during this current vat quarter, so should I account for it all there and pay in this quarter, or do I need to have amended the original invoices (despite them being paid) and pay the vat as part of the original quarters return that it should have been charged in? Also, I am a slow trader and my expenses for the past 2 years will now change as they included VAT in them. Should I re-do/amend those tax returns, or just work out the VAT paid and add it as a lump sum in this current year's self assessment?