British police believe they have thwarted a potential nerve gas attack by the al-Qaeda terrorist network on the country's parliament, a media report said on Sunday.

The plot against the House of Commons, hatched last year, is understood to have been discovered in coded e-mails on computers seized from terror suspects in Britain and Pakistan, The Sunday Times reported.

"Police and MI5 (domestic intelligence agency) then identified an al-Qaeda cell that had carried out extensive research and video-recorded reconnaissance missions in preparation for the attack," it said.

UK blast coverage

The paper claimed that the operation to deter the attack was referred to in an internal police document, detailing a last month meeting of senior police officers, obtained by it.

According to the report, the encrypted e-mails are said to have been decoded with the help of an al-Qaeda "supergrass" who, by revealing the terrorists' code, was also able to help in cracking several more plots.

The discovery of the suspected Commons nerve gas plot was behind the decision to increase security around parliament this summer, the paper said.

A senior officer said the thwarted plot mentioned in the document involved a gas or chemical "dirty bomb" attack upon the parliament. "The House of Commons was one of their targets as well as the Tube (underground network)," he was quoted as saying.

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