There is still no direct, provable link between the July 7 bombings in London and the failed attacks of July 21, Charles Clarke said this morning.

The Home Secretary told BBC radio that while he felt it would be "very, very surprising" if there were not a link between the two groups, the police have yet to formally establish that link "in the judicial sense".

He added: "It’s obvious that there was a group that worked on the 7th of July and another group that worked on the 21st July.

"The extent to which they had support, training, induction and even tasking from outside the groups that actually committed the attacks themselves is something which is being investigated very, very fully and comprehensively.

"I think it would be very, very surprising if they weren’t linked in some way, (but) there is not a direct linkage yet formally established to be able to make that assertion."

Fifty-six people were killed, including four apparent suicide bombers, in the July 7 attacks on three subway trains and a double-decker bus. An attempt to repeat the blasts two weeks later failed when the bombs did not go off.

During the interview on the BBC Radio 4 Today programme, Mr Clarke also clarified his comments yesterday that it would be "absolutely foolish" to assume there will not be a third attack. He said this did not mean that there would be a third attack, but it was essential the authorities and public remain on alert.

The cabinet minister in charge of public security, he returned to work from holiday yesterday, when he was briefed on the state of the investigation by Sir Ian Blair, chief of the Metropolitan Police.

Mr Clarke praised the police investigation and said strong forensic work had produced a "fantastic network of lines of enquiry." But he said the police are a long way from clarifying the full international links of the terrorist movement.

He also refused to be drawn on media reports that there is no CCTV footage of the shooting of innocent Brazilian Jean Charles de Menezes, 27, on July 27 at Stockwell underground station. He said the whole incident was "worrying" and he would await the results of an inquiry into the death.

Last night it emerged that Mr Clarke plans to move against scores of militants accused of stirring up hatred as soon as new immigration rules come into force at the weekend.

The Home Secretary said that further expulsions were imminent and that it would be "absolutely foolish" to assume that there will not be a third terrorist attack in London.

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