That'll probably be the poxy (sorry 'p
roxy'

) servers.
NTL forces a transparent proxy server in the path of HTTP requests and what you get back can be what's cached on the server rather than the latest page. These things are supposed to detect changes, but they're not reliable.
Try CTRL+F5 to force the cache to fetch the page new (though many caches ignore it).
Unfortunately you can't bypass using proxy servers on NTL, but you can try other proxies.
Alternatively, the other possibility is a DNS change. Has the web server's DNS changed recently? If so it can take a while to propogate around the net.