EDINBURGH East Labour MP Gavin Strang today performed another U-turn on his political future and announced he would not, after all, stand at the next general election.
He said he did not have the "mental stamina" for another full term at Westminster.
Dr Strang, who was first elected to the House of Commons in 1970, announced last November he planned to stand down at the next election, pointing out if he stayed on he could still be an MP at 70.
But in March he changed his mind and said he would seek re-election, declaring he was "in it for the long haul". "I'm now 100 per cent sure that I want to continue to represent Edinburgh East," he said at the time.
But today he announced another change of heart. He said: "I told a meeting of Labour Party members in Portobello last night I do not have the mental stamina to be an MP for another six or seven years. I will not be a candidate at the next general election."
Dr Strang, now Scotland's longest serving MP, served as a minister under three Labour Prime Ministers – Harold Wilson, Jim Callaghan and Tony Blair.
And he said quitting the Commons was a big decision.
He said: "It's a great privilege to be an MP. I thought I could carry on for another parliament, assuming I was re-elected, but now I realise I don't feel up to that.
"I'm 65 next month and I have been an MP for 38 years.
"It's a very personal decision. One has only one life and I would like to spend part of it not travelling up and down to London.
"That's final this time."
Dr Strang had a majority of 6202 in Edinburgh East at the last general election in 2005.
But in last year's Scottish Parliament elections, the equivalent constituency, Edinburgh East & Musselburgh, was snatched by the SNP's Kenny MacAskill after the Labour MSP Susan Deacon decided to stand down.
And the Nationalists are expected to make the seat one of their top targets at the Westminster election, expected in two years' time.
The SNP has already selected George Kerevan, a one-time Labour councillor in Edinburgh and now an associate editor of The Scotsman, as its candidate.
But Dr Strang said he was confident Labour could retain the seat. He said: "If you look at the figures, the SNP were third last time and Labour had more than twice the SNP vote."