Update - I've just had a word with my dad, and although I didn't show him any graphs or figures etc, he said that most reviews of ISP's were from unqualified people. He said that most people don't know what they're getting (which is probably true). When I asked "what if the review came from acomputer site" (such as this one), he said that it depends on how many people use that ISP in your area. Therefore any review is probably wrong as it's not form your area.
He went on to say that all or most ISP's use BT's phone lines anyway, so that the services offered will be very similar.
I still don't see why we don't go to Zen if we get more for less there TBH....