Armed police raided the home of two respected foster carers in their hunt for the bomb factory used by the Parsons Green bomber today, just hours after arresting an 18-year-old man close to the port of Dover.

The rapidly moving developments came a day after commuters fled in terror after a homemade bomb partially detonated on a District Line train, injuring 29 people.

Kent police detained the teenager close to the Port of Dover at 7.50am on suspicion of being a terrorist, describing it as a “significant arrest”.

Police officers were later seen searching bins close to Dover Priory rail station a few minutes walk from the port.

The suspect is due to be moved to a south London police station tonight.