Are you registered for VAT? If so you can reclaim, if not you need to contact the inland rev for advice as I am not sure you can. The other thing to keep in mind is that if you are paying it out you also need to charge it.
Working out VAT is fairly easy. as most people have relatively simple affairs. You need a spreadsheet with 3 columns below is an example taken from one of ours for a petrol receipt
05/10/11 Tesco 25.01 4.17 20.84
£25.01 is the gross amount
£4.17 is the VAT
£20.84 is the net amount after VAT taken off.
The VAT is worked out by entering the following formula
=SUM(E89:E89)/1.2*0.2 - e89 refers to the column and row number in which the £25.01 appears in the spread sheet
Net = gross - VAT
You then add up all the VAT you paid out and all the VAT you received and either pay or reclaim the difference.
EG if you paid out £50 VAT and received £25 then you can reclaim £25 VAT.
Expect that is as clear as mud but mess about with a spread sheet its easy when you know how. Once you've got the formula in right just drag it down and it will adjust itself for each row..