A Briton who trained to be a shoe bomber said Osama bin Laden told him shortly after the September 11 2001 attacks that he believed a follow-up terrorist attack could doom the American economy.

Saajid Badat recounted his meeting with the al Qaida founder in videotaped testimony that was played for a federal jury in Brooklyn, New York City.

"So he said the American economy is like a chain," Badat said. "If you break one - one link of the chain, the whole economy will be brought down. So after the September 11 attacks, this operation will ruin the aviation industry and in turn the whole economy will come down."

Badat, 33, was convicted in London in a 2001 plot to down an American Airlines flight from Paris to Miami with explosives hidden in his shoes. His evidence came in the trial of a man accused in a 2009 plot to attack New York's tube network with suicide bombs.

Badat said he was supposed to carry out a simultaneous bombing with failed British shoe-bomber Richard Reid. In testimony recorded last month, Badat said he refused a request to testify in person because he remained under indictment in Boston on charges alleging he conspired with Reid and he has been told he would be arrested if he set foot in the United States.

The videotape of his testimony was played just before the prosecution called to the witness stand a Long Island man who went to Pakistan in 2007 and joined al Qaida forces in an attack against American soldiers.

Bryant Vinas, who says he spent three weeks training with the US Army in 2004 before dropping out because he thought it was too mentally difficult, said he later recommended that al Qaida bomb a Long Island Rail Road train and a Wal-Mart store.

Vinas said he told others in al Qaida in the summer of 2008 that they could leave a suitcase aboard an LIRR train, while explosives could be hidden inside a television that was being returned to a Wal-Mart.

"It would cause a very big economy hit," Vinas said. "Wal-Mart is the largest retail store in the country."

He said he was aware that hundreds of people would die and conceded on cross-examination that he was proud of himself for coming up with the idea. An al Qaida associate suggested it would be more successful if a suicide bomber destroyed the train and a portion of the tunnel through which trains move from Long Island into Manhattan by setting off explosives while in the tunnel, he said.

Vinas, 29, of Patchogue on Long Island, east of New York City, has pleaded guilty to terrorism charges in Brooklyn and become a key government co-operator. The judge who will eventually sentence him watched him testify yesterday.

Vinas said he went to Pakistan in 2007 to find a militant Islamic group and within weeks had latched on to a group that attacked American soldiers in Afghanistan. He said he went on one mission but the group stashed its ammunition and retreated because there were too many planes overhead.

Bothered by altitude sickness, he said, he volunteered to be a suicide bomber but was rejected because he had not undergone enough religious training.

By March 2008, he had linked up with al Qaida, undergoing training for weeks that included theory about explosives and instructions on how to make portions of a suicide bomber's outfit, he said.

Vinas said that he was arrested in Pakistan after leaving the tribal areas because the fighting season was over and he wanted to find a wife.

Although he was testifying at the trial of Adis Madunjanin, Vinas said he did not know the principal characters involved in the plot to attack Manhattan subways in 2009. Medunjanin has denied involvement in the plot.