The man arrested at Gatwick Airport was a Venezuelan national and was believed to be carrying a live grenade, a Metropolitan Police spokesman said tonight.
The north terminal at Gatwick - London's second airport - was shut down today and all flights suspended for a "security alert," an official of the British Airports said.
Earlier today two men were arrested today near Heathrow Airport in London under the Terrorism Act 2000.
The arrests come as British troops continue to guard the airport in an unprecedented move sparked by fears of a terrorist attack.
Home Secretary David Blunkett told the House of Commons today that Britain faced "a real and serious threat" of an attack from al-Qaeda.
Mr Blunkett rejected opposition demands for the government to spell out the exact nature of the alert, saying it was not appropriate to give a "running commentary" of the measures taken at London Heathrow Airport and elsewhere.
"We face a real and serious threat," Mr Blunkett said. "We know that al-Qaeda will try to inflict loss of human life and damage upon us.
"The public must be alert but not alarmed," he said.
AFP, PA