Recently, three British Moslems were convicted of trying to blow up seven airliners using liquid explosives, that would have been smuggled aboard disguised as several different, but normally harmless, chemicals, then detonated once on the aircraft was in flight. During the trial it was revealed that GCHQ (Government Communications Headquarters, the British equivalent of the NSA) devoted "considerable resources" during the police investigation of the plotters. This apparently included tracking down who the plotters were communicating with via email and telephone, especially in Pakistan, and obtaining copies of the messages.
GCHQ personnel are "signals intelligence" (SIGINT) experts, and usually strive to obtain information about enemy electronic communications. GCHQ also has the capability of tapping into the Internet and satellite phones. The British SIGINT experts have long worked with the American NSA on many projects, and constantly share information. This was apparently the case with the liquid bomb investigation, which led to the arrest of the plotters in 2006. But the al Qaeda operative who created the liquid bomb design, was not caught. He's still out there. Al Qaeda provided several hundred thousand dollars for the establishment of a bomb building workshop in Britain, which was raided during the investigation.
The Taliban and al Qaeda are often forced to use electronic communications, because couriers are too slow and vulnerable, and when they do go on the air, there is a good chance that GCHQ or NSA will be listening in. The GCHQ personnel are also with front line units in Afghanistan, to make sure the troops get useful information as soon as possible. Such data often does not age well, and is more valuable the sooner it is used.
Such is also the case with investigations of terrorists who are plotting an attack. Unearthing evidence of the plot, after the attack has taken place, does you little good. So GCHQ has reorganized itself so that, when the need arises, it can pile on to a few subjects, and quickly obtain any electronic communications, decrypting those as needed, and getting the data to the counter-terrorism investigators.