Former British prime minister Gordon Brown is set to announce that he is standing down as an MP, according to reports.

Brown, 63, will soon confirm that he will quit at the general election in May, after playing a key role in the Scottish independence referendum campaign, sources say.

The Labour MP has focused on charity work and his role as United Nations special envoy for global education since his resignation as prime minister in 2010.

An ally told the Sunday Mirror newspaper: "Gordon has confirmed to friends that he will stand down at the election in May.

"He wants to go out on a high after effectively salvaging the campaign to keep the UK together in September. He will focus on his charity work."

Brown was first elected to Parliament in 1983 and was prime minister from 2007 to 2010 and chancellor from 1997 to 2007.

His last-minute intervention in the referendum debate was widely credited with helping the pro-union Better Together campaign to victory.

A timetable he championed for devolving more powers to Scotland was later endorsed by the three UK party leaders in their vow for greater autonomy for the Scottish Parliament in the event of a No vote.