Forensic officers have been searching the mansion block in central London
Police are conducting searches at a mansion block in London in connection with the inquiry into an attempted act of terrorism on a US passenger plane.
Nigerian Umar Farouk Abdulmutallab has been charged with attempting to destroy a plane. He is thought to have been a student at University College London.
Prime Minister Gordon Brown said the UK would take "whatever action was necessary" to protect passengers.
Police have begun sealing off a street in central London linked to the man.
Officers are cordoning off Mansfield Street, in Marylebone, where the he said to have lived in a basement flat owned by his family.
US media have reported that Mr Abdulmutallab, 23, has links to al-Qaeda.
A spokesperson for UCL said a student called Umar Farouk Abdulmutallab was enrolled on a mechanical engineering course between September 2005 and June 2008.
It added: "It must be stressed that the university has no evidence that this is the same person currently being referred to in the media."
Meanwhile, Nigerian banker Alhaji Umaru Mutallab has said his 23-year-old son may be the man connected with the failed incident.
He said his son left London where he was a student to travel but he did not know where he went.
Mr Mutallab said: "I believe he might have been to Yemen, but we are investigating to determine that."
The former minister and chairman of First Bank in Nigeria has left his home in the north of the country to meet security officials in the capital Abuja.
Passengers on the Northwest Airlines Flight 253 operated by Delta on Christmas Day say a man was overpowered after trying to ignite an explosive device as the Airbus 330 approached Detroit from Amsterdam.
According to ABC News in the US, the plot was organised by al-Qaeda leaders in Yemen after the suspect made contact with a radical imam in the country through the internet.
The plane was carrying 278 passengers
They reportedly sewed bomb materials into the suspect's underwear. But federal investigators told ABC the device failed because the detonator was either too small or was not in "proper contact" with the explosive material.
BBC security correspondent Gordon Corera said the British authorities were informed of a possible connection to the UK on Friday evening.
MI5 and police teams assigned to the case are trying ascertain whether Abdul Farouk Abdulmutallab - one of the man's names reported by US media - and Umar Farouk Abdulmutallab are the same person, he added.
It is understood one of their key priorities will also be to check whether the arrested man has cropped up in the course of any other investigations.
UK airport operator BAA said passengers taking flights to the US would face increased searches.
In a statement, BAA said: "Passengers travelling to the United States should expect their airline to carry out additional security checks prior to boarding."
A statement on the British Airways website said Washington has revised its security arrangements for all travellers to the US and they would only be allowed one piece of hand luggage.
A BA spokesman said the directive meant US-bound passengers on all airlines would be subjected to additional screening.
"We apologise to passengers for any delays to their journeys. Safety and security are our top priorities and will not be compromised."
The prime minister said he had been in contact with Sir Paul Stephenson, the Commissioner of the Metropolitan Police, because of the "serious potential threat".
Mr Brown said: "The security of the public must always be our primary concern.
"We have been working closely with the US authorities investigating this incident since it happened."
Home Secretary Alan Johnson said: "We will ensure that the UK continues to have in place the most appropriate security measures to protect the public from the terrorist threat wherever it originates from."
BBC News correspondent Richard Slee said there was fairly low-key police activity at the last known London address of Mr Abdulmutallab, a basement flat in the block near Harley Street.
Flats in the building have sold for up to £2.5m
Reporting from the scene, he said police forensic officers had been seen going into the building.
A blue English Heritage plaque states that philanthropist Sir Robert Mayer once lived in the block where properties have recently sold for between £1.5m and £2.5m.
The Metropolitan Police said its officers were liaising with the US authorities.
A Scotland Yard spokeswoman said: "Searches are being carried out at addresses in central London."