Four men in their 30s have been arrested on suspicion of terrorism.
Officers from Scotland Yard and a regional counter-terrorism police squad arrested the men in Luton this morning.
They are being questioned at a police station in London on suspicion of being involved in the commission, preparation and instigation of acts of terrorism.
Search teams are at seven addresses in Luton.
Scotland Yard said that the swoop is part of an investigation focused on the Luton area, and stressed that it has no connection to the Paris attacks.