The man in North London has been arrested and held under the Terror Act
The 64-year-old man was arrested at a business address and is linked to the terror suspect who was stopped from boarding a flight to Turkey from Stansted Airport on Wednesday.
Neither of the men have been identified but police confirmed they have been detained on suspicion of preparing for acts of terrorism.
Scotland Yard said the arrests are not connected to the Manchester Arena suicide bombing.
On Thursday a warrant was granted to detain the 37-year-old man for further questioning under the Terrorism Act.
Officers have searched a residential address in north London.
Theresa May increased Britain’s terror threat level to critical following an emergency COBRA meeting on Wednesday.
She said the increase meant members of the armed forces could replace police officers in certain responsibilities, allowing these officers to put their efforts elsewhere.
Speaking outside No 10 on Tuesday after an emergency COBRA meeting, she said: “The work undertaken throughout the day has revealed it is a possibility we cannot ignore that there is a wider group of individuals linked to this attack.”
May increased the threat level to critical following the attack in Manchester in Monday…