Police arrested a man in south London overnight as part of their operation to track down those responsible for attacks two week's ago on the transport system in the British capital.
The arrest was the second in the Stockwell area of south London where yesterday a terrorist suspect was shot dead by police.
A police spokeswoman refused to reveal details of those arrested and would not indicate whether either of were among four suspects they have sought the public's help in finding. Closed circuit television pictures of the four suspects were released yesterday with a warning that they may be dangerous.
London has been subjected to two sets of attacks in two weeks. In both cases, four bombs were taken on to three trains and a bus in four locations across the capital.
The first attacks killed 52 people and injured 700 in the worst peacetime attacks in the city's history. And on Thursday the devices failed to go off properly and no one was killed.
The Sunnewspaper today reports the first man arrested was suspected of trying to blow up the bus in Thursday's attempted bombings. Police declined to comment.
The Abu Hafs al Masri Brigade, an al Qaeda-linked group, has claimed responsibility for Thursday's bombings and those of July 7th and has threatened to target Italy, Denmark and the Netherlands, which also have troops in Iraq.
However, the group's claims of responsibility for previous attacks in Europe have been discredited by security experts.
Yesterday's underground shooting sparked a fierce debate over whether police were right to adopt an apparent shoot-to-kill policy in a country where only specialist officers carry weapons.
The Islamic Human Rights Commission and anti-war campaigners condemned the shooting as the start of an unwelcome and dangerous new chapter, but police and London's mayor Ken Livingstone defended it.
"We don't want the situation to develop where the city is so tense that the police are inclined to shoot first and ask questions afterwards," Stop The War campaign said in a statement. But Mr Livingstone said the duty of the police was to protect the public against people considered to be terrorist suspects.
Police said they had followed the man they shot from a house under surveillance and that he had run when challenged. British newspapers said the police were operating under secret new guidelines, codenamed Operation Kratos, which allow them to aim for the head and not the body in case the suspect has a bomb.
Agencies