Downing Street has become heavily fortified since the Irish Republican Army (IRA) attempted to kill former Prime Minister Margaret Thatcher in 1984.
The men were arrested last week following a joint operation by MI5, the UK's counter-terrorism security service, and police.
Security officials believe they have thwarted an alleged plot to assassinate Theresa May by terrorists who would first bomb their way into Downing Street and then kill the prime minister, it has emerged.
In March, five people died in a vehicle attack on Westminster Bridge.
He also found that counterterrorism officials didn't place a so-called ports action on Abedi after he travelled to Libya in April.
Eleven people died when terrorists used vehicles and knives to attack people at London Bridge in June.
Police and intelligence officials thwarted a terrorist plot Tuesday to assassinate British Prime Minister Theresa May, according to a report from United Kingdom -based Sky News. The device landed in the back garden.