In raids across England yesterday anti-terrorism police yesterday arrested 13 men suspected of planning terror acts.

Scotland Yard said the arrests formed part of "inquiries by security services into alleged international terrorism" and that they were part of a "pre-planned, intelligence-led operation".

The Home Office has insisted that there is no threat to an individual target.

But it warned there is a "real and serious" risk of a strike, with security being kept under constant review.

"We are maintaining a state of heightened readiness in the UK," a departmental spokesman said.

"We are taking every feasible precaution to protect British citizens here and abroad and, as ever, we keep the threat level under constant review."

The Guardian reports that David Blunkett is close to backing a specific criminal offence of "acts preparatory to terrorism" as part of his extension of anti-terror legislation planned for this autumn.

The home secretary is expected to introduce the new "broadly drawn" offence of acts preparatory to terrorism alongside the renewal of his emergency powers to detain foreign nationals who are certified as suspected international terrorists.