Transport Secretary Ruth Kelly is to quit British Prime Minister Gordon Brown's Labour government. She told the Labour conference it was time to "step back" from politics and put her family first.

"She indicated... to the Prime Minister that at the next reshuffle he carried out, she would stand down," said Ms Kelly's special adviser.

Media reports said the decision by Ms Kelly, a devout Roman Catholic and mother to four young children, did not appear to be linked to calls for Mr Brown himself to quit over Labour's poor opinion poll ratings less than two years before a parliamentary election. She had been an ally of the Prime Minister but the timing of her departure could overshadow his latest efforts to rally the ruling party behind him.

The adviser said Ms Kelly, who has drawn criticism from some quarters for her links to the Catholic group Opus Dei, would remain in her post for the time being. She could not say when Mr Brown was likely to reshuffle his team. Ms Kelly, now 40, became the youngest minister in the Cabinet when she entered the top echelons of government at the age of 36 after a series of swift promotions through the ranks.

Since then she has held three Cabinet posts - heading the departments of Education and Skills, Communities and Local Government, and finally Transport.