Britons travelling to the US for the New Year were facing long delays today as security was stepped up in the wake of the failed Detroit airliner bomb plot.

As intelligence agencies investigated the former London student nicknamed “The Pope” who allegedly tried to ignite a device on Christmas Day, there were anxious scenes at the US airport last night when a second Nigerian man was arrested on the same route.

A security official at Detroit airport confirmed later the man posed no security risk to the plane. He was a businessman who had become “verbally disruptive” after falling ill on the flight and locking himself in the bathroom for about an hour, the officer said.

Abdulmutallab was released from hospital yesterday into the custody of US marshals at an undisclosed location.

Meanwhile in Britain, passengers waiting to fly to America were hit by delays of up to three and a half hours while urgent investigations took place to find out how Umar Farouk Abdulmutallab – who was known to US and British authorities – was able to take explosives on board a transatlantic airliner carrying 278 passengers.

Scotland Yard detectives continued to search the 23-year-old former University College London student’s luxury apartment in a central London mansion block as it emerged an al Qaida operative in Yemen threatened the US and said “we are carrying a bomb” in a video posted online four days before the attack.

Security sources said police and MI5 were diverting extra staff and resources to the investigation.