Further update
Just got a call from Pipex asking me if I was withdrawing my fault as I hadn't got back to them and she assumed all was well.
I told her all was not well and that BT engineer had just left. I explained that it was BT's equipment from "Green Box" to exchange that wasn't up to the job.
Although I am capped to 1mb from Pipex's end, she explained that I am still connected to the 2mb line at BT's end. I told her a colleague of hers had told me that BT do that to make it easier to be upgraded at a later date. She then said that she would get back on to BT and that I could be changed at BT's end to a 1mb card. She also told me if that doesn't work I would have to go back to 512k package but pay the 1mb rate. I said I would have to move to a different provider as prices were more competitive now and that there is no point paying top dollar for a poorer service.
I am really disappointed with Pipex, as they should have been fighting in my corner with BT rather than leave me to deal with BT on my own, after all I am Pipex's customer and they are obliged to provide me with a service. I shouldn't be arguing with BT about cables, signals, wet weather etc. They are supposed to be the experts but as the BT engineer says, most isps just tell everybody to contact BT as they don't want the expense should it be at their end.