A published report in Britain says authorities believe they foiled a terrorist plot to carry out a nerve gas attack on parliament.

The Sunday Times says an al-Qaida cell in Britain carried out extensive research last year and videotaped reconnaissance in preparation for an attack on parliament and London's subway system.

The newspaper says and internal police security document shows the alleged terrorist plot involved the use of deadly sarin gas and chemical "dirty bombs."

British intelligence officials are reported to have used an al-Qaida informant to crack coded e-mail correspondence found in computers seized from terror suspects in Britain and Pakistan.

The Sunday Times says deciphering the code also helped authorities uncover several terrorist plots.

Police have not commented on the newspaper report.