I know I am replying to an old thread but in case anyone reads this and thinks everything can be backdated for the 4 year period - it cannot.

The 4 year rule applies to goods you still have at point of registration (you may need evidence if questioned).

Anyone who plans to do this should either record invoices at their tax point and then do a journal or adjust the return to account for these (dated within the VAT quarter) this way it will be included in the VAT return.  Alternatively, date them on the first date of the quarter (for identification) include the actual invoice date in description or memo (which I personally prefer) and post them to 'other creditors'.

Once you have the finalised year of accounts and the opening balances for the next year, a journal can be done to adjust any discrepancies on the accounts side.  From that point forth everything should fall into place.

I am not an accountant or claim to be (just work for one).  If you have an Accountant it would be worth getting their advice if you find yourself in this situation.