The government Friday canceled all security passes held by a cleaning company at Heathrow Airport that inadvertently hired journalists as cleaners who used the passes to bypass security and gain access to airliners.

The security crackdown came just weeks after a suspected terrorist bomb blew Pan American World Airways Flight 103 out of the sky over Scotland, killing 270 people, on a flight from Heathrow to New York.Transport Secretary Paul Channon said, "No one at airports in the future should have unsupervised access to aircraft and checked-in baggage in restricted areas unless they have held an airport pass for at least six months."

The airport withdrew all security passes from staff at the company, Skyliner Services.

A London Weekend Television researcher secured a part-time cleaning job with the company by using a false name and references, and Monday night planted a package aboard a Japan Air Lines plane bound for Tokyo. The package was not detected before takeoff.

Graham Dudman, a reporter with The Daily Express, applied for a job with Skyliner Services "as a joke," giving false information and references. He was given a security pass that gave him unrestricted access to areas near the runway and baggage depot.

"I joined a cleaning crew and carried a bulky bag through the checkpoints without being asked to show its contents," Dudman said.

Dudman smuggled an automatic camera into the airport and photographed himself alongside a Pan Am baggage container.

The bomb that exploded Dec. 21, killing 259 on board and 11 people on the ground in Lockerbie, Scotland, was planted in the forward luggage hold, investigators said.