Hate preacher Anjem Choudary is still being questioned by police after being arrested on suspicion of a terrorism offence.
Detectives raided the 56-year-old Choudary’s home in Ilford about 5.40am on Monday.
Scotland Yard counter-terrorism officers arrested a second man - a Canadian national, 28 - who landed at Heathrow on a flight from Canada seven hours later.
Both men were held on suspicion of being members of a banned organisation in contravention of the Terrorism Act 2000.
The pair were being quizzed at a west London police station as police searched three properties in east London.
Choudary, a trained lawyer, was for many years the UK’s most prominent Islamic extremist.
He headed groups, including al-Muhajiroun, which were banned under terror laws introduced in the wake of the 9/11 New York terror attacks and the 7/7 suicide bombings in London in 2005.
Al-Muhajiroun described the 9/11 terrorists as “magnificent martyrs”.
In a statement, the Metropolitan Police said: “Counter-terrorism detectives have arrested two men as part of an investigation into suspected terrorism offences.
“The officers arrested a 56-year-old man from east London in the area at approximately 05.40am.
“They arrested a 28-year-old Canadian national at Heathrow airport at approximately 12.35pm after he arrived on a flight from Canada.
“Both were arrested on suspicion of membership of a proscribed organisation, contrary to section 11 of the Terrorism Act 2000.
“The men are currently being held under section 41 of the Terrorism Act 2000 at a west London police station.
“Police searches of three addresses in east London are ongoing.”