Attention, WH

The original information about the plan came from the Muslim community in Britain, according to a British intelligence official.
The tip resulted from a person who had been concerned about the activities of an acquaintance after the July 7, 2005, terror attacks in London, the official said.

From Guardian:

Pakistan appears to have played a vital role in uncovering the terror plot, helping British security agencies to break the international network. Two or three suspects have been arrested by Pakistani authorities in recent days, but the Pakistan foreign ministry has refused to give details of their identities. It is understood they were"local people" who were arrested in Lahore and Karachi.
An Islamic militant arrested near the Afghan-Pakistan border several weeks ago also provided a lead that played a role in"unearthing the plot", a Pakistani intelligence official said.