After deliberating for more than a week, the nine women and three men remained deadlocked over whether Manfo Kwaku Asiedu and Adel Yahya were involved in the failed suicide bomb plot.

On Monday they convicted four others of conspiracy to murder after a trial at Woolwich Crown Court lasting almost six months.

Muktar Said Ibrahim, Yassin Omar, Ramzi Mohammed and Hussain Osman, who all came to Britain as refugees from war-torn African nations, now face life sentences.

The convictions of the four men, who will be sentenced on wednesday, has led to questions being raised about the role of anti-terrorist police and the security services in the case.

Ibrahim, the leader of the July 21 plot, was allowed to leave the UK while facing charges over extremist behaviour before returning to plot the attack exactly a fortnight after the July 7 terror outrage.

Asiedu and Yahya did not react as the jury was dismissed.

Judge Mr Justice Fulford QC told the nine women and three men, who spent eight days deliberating the case: "Your patience, good humour and perseverance in the face of this lengthy trial has been exemplary. These are only words, but you have my whole-hearted thanks.

"You were told that this trial would last for a maximum period of three months, this trial then doubled in length. Many of you have made significant and personal sacrifices to participate in these proceedings and you have had to make very important decisions having reviewed a huge weight of evidence."

He said none of the jurors would have to take part in jury service again.