LONDON - British police have arrested a third man over the bombing of a busy commuter train in west London last week which injured 30 people.A 25-year-old man was arrested on Tuesday evening in Newport, Wales, the Metropolitan Police said in a statement. Police said they were also searching an address in the town.Two other men who have been detained in connection with the attack remain in police custody."This continues to be a fast-moving investigation. A significant amount of activity has taken place since the attack on Friday," said Dean Haydon, head of the Metropolitan Police's Counter Terrorism Command."We now have three men in custody and searches are continuing at four addresses. Detectives are carrying out extensive inquiries to determine the full facts behind the attack."The home-made bomb went off on Friday during the morning rush hour on a packed train at Parsons Green underground station, engulfing the carriage in flames.On Saturday, police arrested a 18-year-old man in Dover, south-east England, and a 21-year-old in west London over the attack.A total of 36 people have been killed in Britain this year in militant attacks.