Tessa Jowell, the Culture Secretary, has ruled out a public inquiry into the July 7 bombings, warning that it would be an expensive diversion for the police and security services.
Muslim groups and the families of some victims have demanded an investigation similar to the US commission that examined the background to the September 11 attacks. They argue that many questions about last year's bombings remain, including whether intelligence failings contributed to the attacks.
Ms Jowell said she recognised the "raw grief, frustration and anger" of many families, but insisted that an official inquiry could take "years and years" to answer their questions.
"If there was a genuine belief in government that a public inquiry would answer questions which have not yet been answered, then of course it would be held," she told BBC Breakfast. "The concern is that these families would not get the answers to the questions that they seek. There would be an enormous diversion of security resources which need to be directed to prevent this happening again. The costs would be enormous ... money spent on the inquiry that could be spent on better surveillance."
The Government has dug in its heels against an inquiry for months. Last week Tony Blair said that it would divert "resources, energy and commitment from the police and the security services".
John Reid, the Home Secretary, has even argued that it would put lives at risk because of the amount of police and security service time it would consume.
The Home Office has published a narrative of the events and the Parliamentary Intelligence and Security Committee has also examined the background to the bombings.
But critics say no one has scrutinised allegations that one or two of the bombers came to the attention of the security services who then eliminated them from their inquiries.
Nor has there been an official investigation into whether the men acted on their own, whether they had links to al-Qa'ida, and how they became radicalised.
The Liberal Democrats have protested that the two reports were "limited in scope" and are backing a public inquiry.
David Davis, the shadow Home Secretary, has called for an inquiry similar to the Franks Committee, which examined the causes of the Falklands War. He has accepted that some hearings would have to be held in private, but stressed that it should be conducted by a senior independent public figure.