Some ISP's include the VAT charge in their pricing, others will give you the price + VAT. It is always clearly stated on their pricing menu though.
To the best of my knowledge all the ISP's in the UK charge VAT at 17.5% the only exception to this is AOL, they are exempt by having their headquarters and service running from outside the UK. This is about to change though and AOL will have to pay VAT. It's not yet clear if they will absorb this or pass it on to their customers. j.