SCOTLAND Yard believes it has thwarted an al-Qaeda nerve gas attack aimed at ministers and MPs in the British Parliament. The plot, hatched last year, is understood to have been discovered in coded emails on computers seized from terror suspects in Britain and Pakistan. Police and MI5 later identified an al-Qaeda cell that had carried out extensive research and video-recorded reconnaissance missions in preparation for the terror attack. The encrypted emails are said to have been decoded with the assistance of an al-Qaeda "supergrass". By revealing the terrorists' code, he was also able to help MI5 and GCHQ - the...