it was a book for work and as we are an educational department we don't usually pay vat. The invoice had arrived with the vat already included so therefore I had to work this outr before I could send the invoice for payment.
Its true that most but not all books are zero-rated. Some are standard (17.5%) rated.
You can get a full description of this that are and aren't from the VAT Guide (if you have a spare 3 hours) but what you should do is ask for a VAT receipt for the book you bought which will spell out the rate charged and amount, along with their VAT number.