Personally I have always found this box a little odd as its not taken from invoices its calculated by you.

Box 2 Acquisition Tax is calculated as UK VAT due on VAT free purchase of goods from other Member States, i.e. 20% x Box 9 figure, the same amount is then entered in Box 4 (as noted below by HMRC) so the net effect is Zero.

Box 9 Total EU Purchases are the value of goods bought from other EU Member States on a VAT free basis.

The following are HMRC’s instructions:

Box 2: VAT due from you (but not paid) on acquisitions from other EU countries

You need to work out the VAT due – but not yet paid by you – on goods that you buy from other EU countries, and any services directly related to those goods (such as delivery charges). Put the figure in Box 2. You may be able to reclaim this amount, and if so remember to include this figure in your total in Box 4.

Box 4: VAT reclaimable on your purchases

This is the VAT you have been charged on your purchases for use in your business. You should also include:

• VAT due (but not paid) on goods from other EU countries and services directly related to those goods (such as delivery charges) – this is the figure you put in Box 2

http://www.hmrc.gov.uk/vat/managing/returns-accounts/completing-returns.htm#4

If you trade regularly with the EU you may be required to do Intrastat Returns, here is a chart that explains the basics

steve@bicknells.net