As the shock caused yesterday by the attack in London still reverberates across the Atlantic, something has become evident: the United States must be more distrustful of British citizens than of sleeper cells in its own territory or the students coming from madrassas. Since September 11 there have been many examples that have proved that British citizens have organized and participated in attacks.
Why many terrorists come from Great Britain? Many British Muslims are young and poorly integrated into society. They are angry and this makes them vulnerable to extremism. According to a poll, 80% think the war against terrorism is actually a war against Islam and 13% estimates a new attack against the United States would be justified. It is thought that between 10 000 and 15 000 British Muslims are supporters of Bin Laden.
The great permissiveness of British laws regarding the right of asylum and the law related to the granting of visas threaten us. It is easy for the residents of Londonistan to enter in our territory without a verification of the Consulate. Many other European countries have sleeper cells. The European population is declining and is being replaced by Muslim populations. Therefore, we must check our visa policy.

Source
New York Times (United States)

Our Ally, Our Problem”, by Peter Bergen, New York Times, July 8, 2005.