The main prosecution witness at the Old Bailey trial of seven suspected terrorists has revealed he faces 70 years in jail in the US.
In the witness box Babar avoided looking at the defendants
American citizen Mohammed Babar, 31, told the jury he had pleaded guilty to terrorism-related offences in the US.
He said he was giving evidence in the hope his sentence would be reduced.
The seven men, who all come from London and the south-east of England, deny conspiracy to cause explosions between January 2003 and March 2004.
The trial has heard that the men were planning to bomb nightclubs, pubs, trains and shopping centres including the Bluewater in Kent.
Pakistan-born Babar told the jury: "My sole reasons for co-operating was to potentially receive a reduced sentence."
The men, one of whom cannot be pictured, deny all the charges
He said he hoped to be released by the end of next year, but added that any deal would be scrapped if he retracted his statements or was found to have lied in his testimony.
Babar has been flown from prison in America to give evidence against the Britons.
He has told the court how one of the accused, 24-year-old Omar Khyam, said he was working for al-Qaeda.
Prosecutors claimed Mr Khyam and co-accused Salahuddin Amin, 31, from Luton, received training in explosives and use of the poison ricin in Pakistan.
Waheed Mahmood, 34, Jawad Akbar, 22, Mr Khyam and his brother Shujah Mahmood, 19, all of Crawley, West Sussex, each deny a charge of conspiracy to cause explosives.
Denying the same charge are Mr Amin, 23-year-old Anthony Garcia - also known as Rahman Adam - of Ilford, east London, and Nabeel Hussain, 20, of Horley, Surrey.
Mr Khyam, Mr Garcia and Mr Hussain each deny possessing ammonium nitrate fertiliser - a chemical that can be used in bomb-making.
Mr Khyam and Shujah Mahmood deny possessing aluminium powder, also used in bomb-making.
The trial continues.