THE man leading the Coalition's defence of the Union in Scotland has said he is thinking about quitting politics after the General Election.

In a surprise admission, Scottish Secretary Alistair Carmichael said he was considering a career change because he didn't 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 about embarking on it in his fifties.

He told the Sunday Herald: "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 shelflife or future prospects, for fear of looking half-hearted in their current job.

The SNP last night claimed Carmichael's remarks showed he was a "semi-detached" and "apathetic" member of the anti-independence campaign.

Born in Islay, 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 Liberal Democrat MP Michael Moore as Scottish Secretary last October.

Carmichael said it was common for people to go through multiple careers these days.

He told the Sunday Herald: "It's not always regarded as a compliment, but I'm a professional politician. This is my third career. I worked as a waiter and became a hotel manager. I worked in the legal profession.

"Not connected to the referendum, but yes, I think there is a fourth career. I'm not going to be a professional politician for the rest of my life."

Asked if he had identified that career, he went on: "I don't know what it would be yet. But one of the most dangerous things for anybody in politics is to think they're in it for life.

"I look around the political scene, especially at Westminster - I'm not going to name names - but you see people and you think, 'Actually, you've stayed too long'.

"I'm loving the job I'm doing, because it really does matter and it's right at the beating heart of Scottish politics.

" But there is always a risk for every politician that you stay too long, that your shelflife has passed, and you're not fresh about it any more."

Carmichael said he would stand at the next General Election, but after that he might move on. He said: "I'm standing in 2015. My local parties have selected me, so I shall be a candidate.

"But, you know, at the end of that Parliament I will be 54, so maybe at that point I might want to look at something else. I don't know."

SNP MSP Annabelle Ewing said: "With Alistair Carmichael already thinking about his next career move, you have to question his commitment to his current role. This semi-detached attitude shows how apathetic he is already in representing Scotland interests."

Also in today's Sunday Herald, Deputy First Minister Nicola Sturgeon admits she would be "gutted" by a No vote in September.