If they are on ntl, then the website is almost certainly recording the ip address of the proxy server they are being routed through, not their real ip addresses - and this will be the same for the whole area they are in (Nottingham for example).
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That list of proxy servers (in Matt's post) is way out of date - try these ;
http://www.cableforum.co.uk/board/article.php?a=10
or
http://www.cableforum.co.uk/board/article.php?a=11