How do I flag Transactions as being included in a VAT Return so that when / if I have to post earlier transactions they will be picked up in later VAT Returns?

Hello Bugbrookemp, 

Welcome to the Community page, 

The only way to be able to flag a transaction as being in a VAT return is to file that VAT return it falls into. If you have filed a VAT return then anything that is new that is posted with a date before the open return will create exceptions for you.