News, views and top stories in your inbox. Don't miss our must-read newsletter Sign up Thank you for subscribing We have more newsletters Show me See our privacy notice Invalid Email

Two men were stopped boarding US-bound planes at Heathrow days before Britain's terror threat was raised to "severe".

News of the incidents came hours after Home Secretary Alan Johnson lifted the threat level amid fears that al-Qaeda is planning an attack.

The new level, which means an attack is reckoned "highly likely", is second only to "critical".

Security sources say an Egyptian was stopped last Saturday as he tried to board an American Airlines flight to Miami. A man from Saudi Arabia was banned from boarding a United Airlines flight to Chicago the next day and sent back to Saudi.

The incidents and the raised threat level follow the failed Christmas Day bombing on a plane over Detroit.

Anti-terror officials said the past week had seen an "unusually high" number of people on their no-fly list trying to board US-bound planes.

Security is being tightened in Britain ahead of high-level meetings which will see world leaders including Hillary Clinton heading to Britain this week. The US Secretary of State and other leading foreign ministers will be in London on Wednesday and Thursday for summits on Yemen - thought to be a terror haven - and Afghanistan.

Other potential terror targets at the meetings will be Afghan leader Hamid Karzai and United Nations Secretary General Ban-Ki Moon.

In a separate move, Immigration Minister Phil Woolas is to give border police more powers to crack down on bogus students trying to enter Britain. Officials will be able to carry out detailed checks on whether they have enough in their bank accounts to fund their courses.

Part of Manchester Airport's Terminal 3 was evacuated after an Asian man in his 20s tried to take a white powder on to a plane bound for Heathrow. He was not arrested.

Cameron's 'Immigration Con': Page 26

UK THREAT LEVELS

Critical: imminent attack expected

Severe (the current level): an attack is highly likely

Substantial: an attack is a strong possibility

Moderate: attack possible, but is not likely LOW: attack unlikely