Terror plot 'being investigated'

"There is another great (terrorist) plot building up again and we are monitoring this," he told peers during a debate on new security laws.

Lord West, the former head of the Royal Navy, revealed the existence of the plot as the House of Lords continued debating the Counter Terrorism Bill.

He gave no more details of the threat.

His warning came less than 24 hours after peers forced the Government to abandon plans to extend maximum pre-charge detention for terror suspects to 42 days.

Home Secretary Jacqui Smith dropped the measure from the Bill after it was defeated in the upper house by 191 votes.

But she warned critics that they were exposing the country to a greater risk.

Shadow home secretary Dominic Grieve later described Lord West's comments as "reckless in the extreme".

"We are told the police have to strike a balance between early arrest during a developing terrorist conspiracy in order to protect the public, and waiting long enough to ensure there is enough evidence to secure a conviction," Mr Grieve said. "The minister's comments give us the worst of all worlds - cutting across both objectives."

A Home Office spokesman said: "We have always been clear - as has the director general of the Security Service (MI5) - that there are many plots, individuals and groups under investigation. We don't elaborate on specific plots or individuals."