A London Underground sign is seen behind a locked gate, in central London December 26, 2010. Credit: ReutersLondon: A second man has been arrested over Friday’s bomb attack on a London underground train that injured 30 people, police said.The 21-year-old man was arrested in the west London suburb of Hounslow just before midnight on Saturday, the Metropolitan Police force said in a statement.He was detained under Britain’s Terrorism Act and taken to a south London police station, the force added.Earlier on Saturday, British police arrested an 18-year-old man in the port of Dover and raided a property in Sunbury, a small town outside London, as they hunted for whoever planted the device.Hounslow is about four miles from Sunbury where police raided and searched a building on Saturday in connection with the bombing.The home-made bomb shot flames through a packed train carriage at west London’s Parsons Green train station but apparently failed to detonate fully.(Reuters)