Four men arrested for 'preparing acts of terrorism' in London terror raids

British police have arrested four men in a series of raids on Wednesday in east London on suspicion of preparing terrorist attacks in the United Kingdom.  

Special branch officers, the London Metropolitan Police's counter-terrorism unit, had detained the four men, aged 18, 24, 25 and 27, at their homes in east London. 

"These arrests were pre-planned as part of an ongoing investigation by the Met's Counter Terrorism Command and (the domestic spy agency) MI5," police said in a statement.

"The arrests are linked to activity in the UK."

The men were being questioned at a south London police station "on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism", the statement added.

Britain has been on its second-highest alert level of "severe" since August 2014, meaning an attack by militants is considered highly likely.

In March, a man killed five people after driving into a crowd of pedestrians on Westminster Bridge in central London before stabbing a police officer in the grounds of parliament. 

He was shot dead at the scene.

Earlier this month police charged three women from London with preparation of a terrorist act and conspiracy to murder after a raid in which one of the women was shot by armed officers.

In another incident last month, a man was arrested on Parliament Street, near the House of Westminster and UK Prime Minister Theresa May's Downing Street office, and later charged with terrorism and explosives offences.