A Briton plotted with "shoe-bomber" Richard Reid to bring down two packed US-bound planes at the same time, the Old Bailey heard today.

But Saajid Badat, 25, from Gloucester, pulled out days before the attack and took apart his own bomb, prosecutors said.

In a surprise turn-around, Badat pleaded guilty to conspiring between January 1, 1999, and November 28, 2003, to place a device on an aircraft in service.

Badat's trial was due to start today, but he changed his plea to guilty. He is the first person in the UK to be convicted of a terrorism offence since 9/11.

Intelligence services believe Badat had been colluding with fellow Briton Reid, who was jailed in America for trying unsuccessfully to ignite a shoe bomb on board a US-bound jet.

Prosecutors said Belgian telephone cards found on Reid were used by Badat to contact Reid's terrorist contact Nizar Trabelsi. The go-between, who is in prison in Belgium, was arrested in September 2001 and convicted for planning to attack an American base in the European country.

Badat agreed to be a suicide bomber on a passenger plane while in the air from Europe to the US, prosecutor Richard Horwell told the court today.

He was trained in Pakistan and Afghanistan, where he received a bomb identical to the one used by Reid as he tried to blow up a flight to Miami on December 22, 2001.

The prosecution said Badat had confessed to the plot on the way to the police station, but later withdrew.

He had booked a ticket from Manchester to Amsterdam, from where he would have flown to the US. Yet he never took the flight.

Two years later Scotland Yard's counter-terrorist branch found the device in Badat's Gloucester family home when they detained him in November 2003.

The plastic explosive, an amount smaller than a man's fist, was wrapped in a sock inside a dark suitcase police found on the landing of the house in St James Street.

He had separated the explosive from the detonator, which was found in another suitcase hidden underneath Badat's bed.

Although the bomb was never placed in a set of shoes, forensic tests proved the orange detonating cord to be an exact match of the cord in Reid's device.

Another link between Reid and Badat is the identically forged exit stamps from Pakistan in their British passports.

Like Reid, Badat is a British-born Muslim convert. He studied at a Mosque in Blackburn.

Met anti-terrorist chief Peter Clark said the conviction followed three years of "painstaking" investigation by agencies around the world. "We travelled to some 15 countries as part of the investigation and gathered overwhelming evidence which lead to Sajid Badat pleading guilty today."

It also showed the seriousness of the terror threat, he added. "Badat had agreed to blow up a passenger aircraft from Europe to the United States and was prepared to kill himself and hundreds of innocent people.

"We must ask how a young British man was transformed from an intelligent, articulate person who was well respected, into a person who has pleaded guilty to one of the most serious crimes that you can think of."

Badat, who could be jailed for life, will be sentenced on May 18.