Paradoxically, unless banned directly by IP, it would probably pass what are termed "high anonymity" proxies...
The definition I found (I'd never heard the term before), was an anonymous proxy that does NOT give any evidence of being a proxy (other than if too many people come from one address, that may be a problem) - the standard anonymous proxy does admit to being a proxy.
MODS, please remove this if you'd rather, as I'm reluctant to make these easier to find, but:
http://www.aliveproxy.com/high-anonymity-proxy-list/
Open, high anonymity proxies - check one against your favourite proxy checker (eg. all-nettools) and it should NOT be able to detect a proxy.
Since you cannot escape proxying with NTL, this may be the only way to enter a site with a "no proxies" rule - you can see why I had second thouts before posting the link, as they make it very easy to subvert IP based access restrictions.