A man was arrested yesterday at Gatwick airport with what was believed to be a live hand grenade after arriving on a British Airways flight from Colombia.

The north terminal was closed and evacuated.

Armed troops are still guarding Heathrow - where two men were arrested yesterday during searches of cars - and extra security measures are also in place at Stansted.

David Blunkett, the home secretary, said the arrests showed that the terrorist threat was real.

"First, it reinforces that we really do have a problem as people have been saying that it doesn't exist," he said.

"Second, it means that our security services are on the ball. Third, over the next few days we need to follow these leads through."