The relevant text is as follows:

It is sometimes suggested that one way of dealing with unlawful file sharing is to block all of the Internet traffic associated with it, and in particular to block any access to websites which are involved in the stages prior to the actual file transfer. It is usual to point at the supposed success of the Internet Watch Foundation (IWF) blocking list for child sexual abuse image websites. The comparison is flawed – and in any case the blocking of IWF sites is trivial to evade. It is my view that the main impact of any attempt to use blocking systems to prevent unlawful file sharing would be to bring evasion techniques into everyday parlance, and in the process the very limited impact of
the IWF initiative would be entirely undermined.