In what appears to have been a renewed investigation, a witness gave detectives in January 2005 part of Mohammad Sidique Khan's name, his mobile telephone number and the name and the address of his mother-in-law. The revelation suggests Khan was being investigated much nearer to the London bombings than has been officially admitted.

Details of how Khan and a second bomber, Shehzad Tanweer, came repeatedly under surveillance in 2004 were disclosed this week after five of their associates were jailed for life for planning attacks around south-east England.

The discovery that Khan was reinvestigated the following year appears to contradict claims from MI5 that inquiries about him came to an end in 2004 after it was decided that other terrorism suspects warranted more urgent investigation. It is also likely to lead to scrutiny of MI5's assertion that its officers, who had followed, photographed and secretly recorded Khan, and made other inquiries about him, did not know who he was.

The Guardian has learned that on January 27 2005, police took a statement from the manager of a garage in Leeds which had loaned Khan a courtesy car while his vehicle was being repaired. MI5 had followed Khan and Tanweer as they drove the courtesy car across London in March the previous year. The garage manager told police that the car had been loaned to a "Mr S Khan" who gave his mobile telephone number and an address in Gregory Street, Batley, West Yorkshire.

Khan, the police were told, had asked for his repaired car to be delivered to another address, in nearby Dewsbury, which is now known to be his mother-in-law's home. Almost a year earlier, MI5 officers had followed Khan to the same address after watching him meet a number of suspected terrorists.

That was not the end of police interest in Khan in 2005. On the afternoon of February 3 an officer from Scotland Yard's anti-terrorism branch carried out inquiries with the company which had insured a car in which Khan was seen driving almost a year earlier. He discovered that Khan had insured a five-door silver Honda Accord saloon, in his own name. Inquiries also showed that the car was registered in the name of Khan's mother-in-law.

Nothing about these inquiries appeared in the report by parliament's intelligence and security committee after it investigated the July 7 attacks. The shadow home secretary, David Davis, said: "It is becoming more and more clear that the story presented to the public and parliament is at odds with the facts."

Scotland Yard described the 2005 inquiries as "routine", while security sources said they were related to the fertiliser bomb plot.

In the Commons yesterday, Tony Blair said an independent inquiry would "undermine support" for the security service. David Cameron said only a full inquiry would "get to the truth".

There was more confusion yesterday over evidence that Shehzad Tanweer was surfing the internet for bomb-making tips in June 2005, two weeks before the suicide attacks. According to a document which prosecution lawyers in the fertiliser bomb plot case disclosed to the defence before the trial began, Tanweer was heard to be discussing bombings and using the internet to make such a bomb.

The document says: "Tanweer told the same person he had entered Afghanistan and met people from around the world who had got into his head." MI5 says this information is "false". But the Crown Prosecution Service told the Guardian the information was passed to it by Scotland Yard. The Yard does not deny this but says its officers in the case had "no recollection" of the information.