Spymasters warned Tony Blair before the July 7 homicide bombings that Al Qaeda was planning a "high priority" attack specifically aimed at the London Tube.

A leaked four-page report by the Joint Intelligence Committee (JIC), which oversees all spying, is the first definitive evidence that the intelligence services expected terrorists to strike at the Underground.

The disclosure will fuel critics’ suspicions that Blair decided to rule out a public inquiry into the bombings last week because it could expose intelligence failings at the highest level. The document, marked Top Secret and signed off by the heads of MI5, MI6 and GCHQ, the government eavesdropping center, was based partly on the interrogation of Khalid Sheikh Mohammed, Al Qaeda’s then operations chief.

It stated: "The UK and its interests remain high in Al Qaeda’s priorities . . . Plans have been considered to attack Heathrow, the London Underground and other targets."

Ministers and senior security officials have insisted that there was no warning of an imminent attack ahead of the July 7 bombings, in which 56 people died.

While technically true, the leaked document dated April, 2003, will be seized on by critics to show that ministers failed to disclose that they knew Al Qaeda was targeting the Tube.

A statement in September 2003 by the prime minister and Sir John Stevens, the then Metropolitan police commissioner, that a homicide attack was "inevitable", did not name the Tube as a specific target.

The performance of MI5 has already been criticised because it lost track of Mohammad Sidique Khan, leader of the terror gang, whom it placed under temporary surveillance 18 months before the bombings.

Officers judged that Khan was not an immediate threat to national security and decided to stop monitoring him.

Blair ruled out a public inquiry on the grounds that it would detract from the investigation into the July 7 bombs and the failed July 21 attacks. The report dated April 2, 2003 is entitled International Terrorism: The Current Threat from Islamic Extremists. Mohammed, who organised the 9/11 attacks, had been arrested in Pakistan the previous month.

In a key passage it states: "The UK and its interests remain high in Al Qaeda’s priorities. Interrogation of Khalid Sheikh Mohammed and other detainees confirms this. "It shows that plans have been considered to attack Heathrow, the London Underground and other targets."

The report adds that terrorist suspects with links to east Africa are under surveillance. "We do not yet know the full nature of their activity, but they do not appear to be planning attacks here (some were questioned by the police)."

Five men have been charged over the July 21 attacks. Four of them came from either Ethiopia, Eritrea or Somalia.

JIC documents are circulated to a small group of senior ministers. These include the home secretary, the foreign secretary and defence secretary as well as top civil servants in Whitehall.

The Tories demanded the government publish the whole JIC document and disclose what other intelligence there had been about threats to the Tube. Patrick Mercer, the party’s homeland security spokesman, said: "This leak underlines our demand for an independent inquiry."

The police would consider shooting civilians to prevent contaminated people leaving a cordoned-off area in a radiological, biological, nuclear or chemical attack, Chris Fox, president of the Association of Chief Police Officers, has said.