FOUR failed suicide bombers who are determined to commit mass murder and die rather than be taken alive were being hunted by police last night.

A suspected accomplice was shot dead in front of passengers after being cornered by a team of Scotland Yard marksmen as he fled on to an Underground train at Stockwell station in South London. It is understood that the dead man was not carrying a bomb.

The four men, determined to be seen as martyrs and terrify the public by disclosing that they were British, left clues to their identities in the backpacks that failed to explode on Thursday. Police are taking seriously the possibility that the gang may be equipped with ingredients for a “dirty” bomb using biological, chemical or radioactive materials and that there could be a “rolling programme” of further waves of suicide bombings.

A man was arrested last night in Stockwell in connection with the attacks. Neighbours described how police surrounded a block of flats to arrest the suspect, who was thought to be from Ethiopia. Police refused to comment on the man’s role but sources said he was a possible member of the bombing team. Reports that he was suspected of attempting to blow up the No 26 bus in Hackney could not be confirmed. Another man was later taken away and arrested from the same flat.

The Government fears that Britain faces the prospect of years of terror from religious fanatics motivated by a desire to establish a worldwide Islamic state. Tony Blair, at Chequers last night, was briefed by members of the Cobra emergency committee as ministers prepared to recall Parliament if the situation gets any worse.

President Bush tried to boost morale, saying that the “people of Great Britain must understand how strong the Americans stand with them during these trying times.

“I am confident, like our country, that the citizens of that country will not be intimidated by thugs and assassins.”

A group linked to al-Qaeda claimed responsibility for the attempted bomb attacks in London on Thursday and gave warning that they would continue with their mission until Britain pulled out of Iraq. The Abu Hafs Brigades said: “Our strikes in the heart of the British infidel capital are nothing more than a message to all European governments that we shall not relent until all infidel forces quit Iraq. This is a warning to all those who follow the policies of the President of infidel America.”

Suspected faces of the London-based cell, recorded by CCTV cameras, were released by police. Members of the public who see the suspects were urged to dial 999 but not to approach them. Sir Ian Blair, the Metropolitan Police Commissioner, admitted that this was the “greatest operational challenge ever faced by Scotland Yard”. His officers were facing “previously unknown threats and great danger”.

Elite detectives, dressed as young Londoners with peace wristbands, designer leisurewear and fashionable haircuts, are now on the front line, stalking suspects. Trained with the SAS in close-combat techniques, they are equipped with brutally efficient, adapted Heckler & Koch pistols.

Raids took place across the capital yesterday at addresses with possible links to the bombers. Neighbours saw armed officers, their faces hidden by gas masks, scale walls and swarm through gardens.

A man was arrested at Snow Hill station in Birmingham and two suitcases were dealt with by explosives officers. The station was evacuated. Two hours later, British Transport Police declared the incident over.

Earlier, the brutal new reality of life in the capital was brought home to passengers on the Northern Line train that arrived at Stockwell station. Plain-clothed police had been trailing an Asian man from an address traced through information left in one of the rucksacks. The suspect was believed to be intimately involved in the terror gang and detectives hoped that he would lead them to the culprits. The dead man wore a heavy, padded jacket at odds with the mild weather. When he went into the station, officers gave chase. He leapt over barriers but tripped as he boarded a train.

Mark Whitby, a passenger, said. “He looked absolutely petrified. He half-tripped and was half-pushed to the floor and the policeman nearest to me had the black automatic pistol in his left hand. He held it down to the guy and unloaded five shots into him.”

The first man arrested in connection with the July 7 bombings was released without charge last night. The man aged 29 was arrested on July 12. Scotland Yard said: “A man arrested in West Yorkshire on suspicion of the commission, instigation or preparation of acts of terrorism was released with no further action.”

THE MANHUNT

9.45am Suspect followed by police from address in Stockwell towards Tube station

10am Suspect shot on Northern Line train at Stockwell station

1pm Police raid house in West Kilburn near station where Shepherds Bush bomber boarded train

3.30pm CCTV photographs released of suspects in Thursday’s failed bomb attacks

5pm Man arrested at Corfe House, Stockwell 5.05pm Police say that man killed at Stockwell was not one of four pictured suspects

5.55pm Man arrested at Snow Hill in Birmingham. Station evacuated and suitcases examined

8.15pm Snow Hill reopens, incident is declared over

10.20pm: Another man is taken away from Corfe House for questioning

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