Counter-terrorism police said they have detained two men at Stansted Airport.
A 34-year-old man from Kuwait and a 48-year-old man from Italy were detained by counter-terrorism officers from the Eastern Region Special Operations Unit soon after 7pm on Sunday, the Unit said in a statement.
The two men had arrived on a flight from Vienna and were detained under Schedule 7 of the Terrorism Act, police said.
The BBC has reported the plane was intercepted by RAF Typhoon jets following unconfirmed reports of a security threat on board.
Air monitoring agency Mil Radar tweeted at around 7.30pm that two Typhoons had been launched from RAF Coningsby, with tracking showing they had circled in the Stansted area.
Police say their enquiries are continuing.