A shoe bomber who was jailed for 13 years for trying to blow up an airliner has had his sentence cut by two years after agreeing to give evidence against other suspected terrorists, police and prosecutors said today.

Saajid Muhammad Badat, who was jailed in 2005, saw his prison sentence reduced to 11 years in 2009 as part of a deal with prosecutors, it can be reported today.

It is the first time in the UK that a convicted terrorist has entered into an agreement with the Crown Prosecution Service to give evidence in a trial against other alleged terrorists.

In a statement Sue Hemming, Head of the CPS Special Crime and Counter Terrorism Division, said the agreement with Saajid Muhammad Badat had not been entered into lightly.

"We considered very carefully the merits of entering into this agreement with a convicted terrorist, and we believe that the administration of justice internationally benefits from such an agreement.

"This trial is the first time a UK convicted terrorist, has agreed, under the terms of our agreement, to give evidence in the United States. This will be in the trial, opening today in New York, of Adis Medunjanin, relating to an alleged al-Qaeda martyrdom plot in New York from 2008-2010.

"Badat has helped with investigations in this country, he continues to co-operate and has agreed to testify in other trials if called upon."

Deputy Assistant Commissioner Stuart Osborne, the senior national co-ordinator for counter terrorism said: "This case is an example where the Socpa (Serious and Organised Crime and Police Act 2005) legislation has secured substantial and significant evidence and intelligence relating to investigations undertaken by the counter terrorism command which has also assisted law enforcement agencies in other countries."

Badat's sentence was reduced to 11 years on November 13 2009, but an order banning reporting of the deal was put in place, for Badat's safety, until he was due to give evidence in public, the CPS said. It has now been lifted.

When Badat was jailed in April 2005, a judge said he had to be given credit for turning his back on terrorism.

Mr Justice Fulford said 25-year-old Badat could have been facing a term of more than 50 years if he had gone ahead with the plan to blow up a passenger jet.

But he added: "It would not be in the public interest to send out a message that if would-be terrorist turn away from death and destruction before any lives are put at risk, the courts will not reflect in a significant and real way any such genuine change of heart in the sentence which is handed down."

Badat, of Gloucester, had admitted plotting to explode a shoebomb on a transatlantic flight in December 2001 at the same time as fellow shoebomber Richard Reid.

But the court was told he could not face being a "courier of death" and rejected terrorism.

The dismantled device was found in two suitcases at Badat's family home two years later in November 2003 when he was arrested.

It was found to be identical to Reid's shoebomb, which he failed to ignite mid-air, and he was later jailed for life in America.

Badat admitted training in Afghanistan where he had been recruited and given the shoebomb before returning to Amsterdam at the same time as Reid.

But Badat returned to the UK - still wearing the shoebomb on his feet - and never flew to the US.

He dismantled the device and emailed his handlers saying he had pulled out.