In a surprise admission, Scottish Secretary Alistair Carmichael said he was considering a career change because he did not want to become stale like some of his Westminster colleagues.
The 48-year-old, who was a hotelier and a lawyer before becoming the Liberal Democrat MP for Orkney and Shetland in 2001, said he felt yet another career beckoned for him, and he was thinking of embarking on it in his 50s.
He said: "Not connected to the referendum, but I think there is a fourth career. I'm not going to be a professional politician for the rest of my life."
It is rare for a senior politician to discuss their shelf-life or future prospects, for fear of looking half-hearted in their current job.
The SNP claimed Mr Carmichael's remarks showed he was a "semi-detached" and "apathetic" member of the anti-independence campaign.
SNP MSP Annabelle Ewing said: "If Alistair Carmichael is already thinking about his next career move it's no surprise people are questioning his commitment to his current role.
"This semi-detached attitude shows how apathetic he is already in representing Scotland interests.
"During his short time as Westminster's man in Scotland, Mr Carmichael has repeatedly failed to stand up for the people of Scotland. People in Scotland have far greater expectations than this and Alistair Carmichael urgently needs to up his game when it comes to standing up for Scotland."
Born in Islay, Mr Carmichael worked as a hotel manager in the late 1980s before studying law.
He was a procurator fiscal depute in the early 1990s in Aberdeen and Edinburgh, then a defence solicitor until his election in 2001.
After the Coalition formed in 2010, he become the LibDems' chief whip, in charge of discipline among his party colleagues. He replaced fellow LibDem MP Michael Moore as Scottish Secretary last October.