Thanks for all the advice. I tried the MTU suggestion but it didn't make a difference.
However, I think I've just found a solution.
There might be a design flaw on Cisco's part on the X3000 router. The router is able to block cookies, ActiveX and proxy etc if I wanted to. Obviously I did not select any of them because I don't want anything to be blocked.
I have just gone back and I thought I put a tick on all of them and see whether they will show me anything on the firewall log. Bang, all the websites work fine now. It seems to me that even though the GUI says ticking the box means blocking that particular traffic, by ticking the box the router would allow traffic instead.
A silly design flaw made by a world-class company. Oh well, at least it's working fine now.
Edited by snakieuk (Fri 02-Nov-12 20:45:08)