The threat of a terrorist strike has been downgraded from severe to substantial, putting the risk of an attack at the lowest level since just before 7/7.

But Alan Johnson, the Home Secretary, said that the country still faces a “real and serious” threat from terrorists.

Mr Johnson said: “The Joint Terrorism Analysis Centre (JTAC) has reduced the threat to the UK from international terrorism from Severe to Substantial.

“This means that an attack on the UK is a ‘strong possibility’. JTAC make their judgments based on a broad range of factors, including the intent and capabilities of international terrorist groups in the UK.

“We still face a real and serious threat from terrorists and the public will notice little difference in the security measures that are in place and I urge the public to remain vigilant.

“The police and security services are continuing in their thorough efforts to discover, track and disrupt terrorist activity.”

This month, the country’s most senior counter-terrorism officer, John Yates, hinted at the possibility of a change.

He told the Association of Chief Police Officers’ conference in Manchester: “I think there is a possibility the threat level may come down. It is logical because we cannot keep having it high unless the threat is there.”

Just after the attacks on the transport system in July 2005 the threat was raised to critical, as it was again after the Haymarket and Glasgow airport attacks in June 2007 before being downgraded back to severe where it has remained until today.

The decision to lower the threat level comes as the Metropolitan police, Britain’s biggest force, announced that it will limit its use of controversial stop-and-search powers amid claims of discrimination against minority groups.

Although all of London is still designated a stop-and-search area by the Home Secretary where Section 44 can be used, from today the areas where it will actually be used have been scaled back.

Officers can stop and search a person or a vehicle under Section 44 around specific and iconic sites, such as Buckingham Palace and Parliament, and during specific operations.

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