Well I finally worked out what the problem was and Chrysalis was right it was the router, I hooked up a laptop with ICS and the problem went away (although this was connecting the modem via USB which will reduce the speed anyway so could just mask the problem). It turns out I have 3 routers (I got a Belkin router since my last post

) that do not support 10MB on the WAN port, I bought a new router a Linksys WRT54G and this fixed my problem.
I did phone NTL tech support since I last posted and I have to say I'm extremely disappointed that they could not work this out from the information I provided. I explicitly pointed out to them (though I don't think I did in this thread) that the problem only seemed to have appeared since the 10MB upgrade. I'd run the ICS test by them and also pointed out that connecting a single machine did not have a problem (USB or ethernet) so the fault was always pointing at modem to router communication. It was their upgrade to 10MB that caused the problem surely they should have anticipated this? Or if not I'm sure they've had plenty of similar phone calls already yet the possible fault is not on the tech support script (Or else I got a very unhelpful operator).
Anyway I'll take the time to use the feedback form NTL provide for this, though I should also point out that the service I recieved from customer support was a pleasant surprise. The operator was friendly and helpful and I got absolutely no quibble about replacing my NTL modem, I asked for an upgrade they said fine (after a search through my records I believe

) and an engineer had been and upgraded it within 4 days. 2 out of 10 for tech support but 9 out of 10 for customer services.
Talifer