LONDON, AUG 10, SPA -- Major delays are expected at all UK airports after the nation's threat level was raised to "critical" Thursday when police disrupted an apparent plot to blow up planes in mid-flight. The highest possible alert level, raised by the British Home Office, means "an attack is expected imminently," and authorities have said no hand luggage would be allowed onto planes. London's Metropolitan Police said a months-long intelligence operation by the anti-terrorist branch and security service resulted in several arrests overnight, according to a Scotland Yard news release. The aim of the alleged plot was to explode devices carried aboard planes in handheld luggage -- especially on flights from Britain to the United States, according to Scotland Yard."This is a major operation which inevitably will be lengthy and complex," Scotland Yard said in a statement, according to a report of CNN. Britain's Home Secretary John Reid called the alleged plot significant and said it was designed to "bring down a number of aircraft through mid-flight explosions, causing a considerable loss of life.""We are doing everything possible to disrupt any further terrorist activity. This will mean major disruption at all UK airports," Reid said, adding the move to raise the alert level was "precautionary."--SPA www.spa.gov.sa/381921