Channel Tunnel 'under threat of attack'

The alleged plot came to the attention of the French overseas intelligence service the DGSE, possibly via the US Central Intelligence Agency, and was detailed in a secret December 19 report to the Paris government.

French and British intelligence services have since run checks of security systems protecting the 31-mile (50-kilometre) tunnel but the DGSE warned that the threat level remains high, the newspaper said.

Even before the alleged threat, British security services were on the second-highest alert -- "severe" -- following what police said was an attempt by Islamist militants to blow up transatlantic passenger jets in August.