d'oh working in IT support, I should know to take everything the customer tells me with a pinch of salt, and not believe them until I've started from the beginning myself
so, I go into the loft, there 2 cables, one brown, one white coming from the aerial.
Me: Where do those leads go?
neighbour: the white one down through a hole in the ceiling through the airing cupboard for the spare room tv, the brown down through to ground floor, where there's a splitter for the front room, and back room.
me: err, you said the splitter was by the upstairs tv to go to the downstairs one.
Behind the bookcase in the living room, is an aerial wall socket, lead from that goes to a mains powered booster box, with a splitter in one output. the living room tv he just uses the Virgin box, the lead from the splitter goes through the wall to dining room.
so, he moved the bookcase and found that the lead going into wall was a bit loose, so he pushed it in, I retuned living room tv, and dining room VCR/DVDR and got signal rating 10 and a good picture
So, glad we fixed it with something easy, just a shame he hadn't explained/didn't know his setup properly