London (Agencies): According to documents released by WikiLeaks, home-grown suicide bombers who are not on the radar of intelligence agencies are a bigger threat to Britain. Also the danger is not expected to abate "anytime soon," counter-intelligence officials in the UK have warned.

The bombers, who pose a "unique" threat to Britain, are from a generation of 'home-grown terrorists' trained to become "suicide operatives," British intelligence agency MI6 has warned.

The warning was sounded in a private briefing from a senior MI6 official to visiting American Congressmen amid growing US fears over the radicalisation of young British Muslims.

These British-born radicals will leave the authorities "hard pressed" to prevent an attack, according to a top counter terrorism official at the Secret Intelligence Service.

The leaked documents also highlight American government concerns that the British intelligence services are struggling to combat these extremists because of budget cuts and a wave of lawsuits from terror suspects.

William Hague, the Foreign Secretary, announced further cuts to the counter-terrorism budget earlier this week.

Details of the warnings are contained in diplomatic dispatches from the cache of tens of thousands of US embassy cables leaked to WikiLeaks and passed to The Daily Telegraph.

The WikiLeaks files suggest Britain faces threats from both foreign and domestic extremists.

They detail mounting American concern over the inability of British security forces to apprehend terrorist’s intent on launching attacks on the West.

Yesterday, Lord Carlile, the independent reviewer of counter-terrorism legislation, said there was now a "relatively low legal threshold" for a suspect to avoid deportation in domestic courts.

The European Court of Human Rights has rejected the Government's argument that the risk of a deportee being ill-treated in his home country should be balanced against the threat they pose to Britain's national security if they were to remain in the UK.

"The effect is to make the UK a safe haven for some individuals whose determination is to damage the UK and its citizens," he said.