Tower Hamlets councillor Oliur Rahman, a Left List candidate in the 1 May London Assembly elections, was detained at Heathrow airport under the Prevention of Terrorism Act.
He was questioned about why he attended the Sixth Cairo international anti-war conference, held in Egypt last week.
The Cairo Conference has been a central rallying point for anti-war activists and a focus of opposition to the repressive Egyptian regime of President Hosni Mubarak.
It appears that while Oliur can travel to a political conference in a dictatorship to meet other peace activists, he cannot come through Heathrow without being held and harassed by Gordon Brown’s secret police.
He has now been released. More news to follow.