Just an update. Since this afternoon my PC has been directly connected to the modem, no proxy specified in IE and no firewall. At 19:20 - 19:30 the problem resurfaced. For most of that time I was again unable to view about 50%+ of websites. I was able to get to bbc.co.uk and
http://tamb.ipbhost.com (tartan army website).
Was unable to get to trickery.net, wireplay.co.uk, overclockers uk and here (although this may have been down anyway at the time not sure). In each case the browser would go looking for the site then come back with webpage not found.
I'm confident its not my router as the problem occured when it wasn't being used. I'm confident its not my firewall. I'm confident its not any virii or software glitches. Its impossible though to get through to NTL BB tech support in time. As by the time I've waited in the queue the problem has resolved itself. It just seems that something in the renfrew ubr is having an intermittent fault and taking 5-10 minutes to rectify itself, reboot or whatever. No idea what it could be.
It just seems I'm destined to have this problem forever as nobody is able to check anything it seems and short of using my DV Cam to show the problem I'm not sure anyone is actually going to see it in action.