Don’t worry. I know exactly where to overtake on these roads. I know them like the back of my hand,” Viscount Thurso says as, rally driver-like, he speeds to within inches of the car bumper in front and whooshes into a blind dip.

It is about three hours since the cigar-loving John Sinclair, Third Viscount of Thurso, has had a smoke, having left the House of Commons at lunchtime for Gatwick to fly to his constituency in Caithness in the northeast of Scotland.

Now, stumpy Villiger cigar in mouth, the immaculate Brylcreemed, walrus-bearded, Lord Lucan-lookalike is driving fast across the Caithness heathers, forked with mid-summer lightning flashes, leaving Westminster behind him and with a few days’ break ahead.

Lord Thurso — known as John to almost everyone — has two great leisure pursuits: fishing on his estate, where his family have lived for generations; and tending his vegetable patch. And it is to the cabbages, cos lettuces, clumps of artichokes and gooseberries that he is headed.

“There’s only two ways into Thurso — up the coast or from the North; there’s nothing in the middle, but I do own a big slice of that middle bit.”

“I am behind on the vegetables,” Lord Thurso complains, exhaling smoke from a 4in cigar, which he chain smokes in the evenings. “It’s very difficult to get on top of the gardening here. You can’t do anything in March, it’s too damned cold. This year, April was so mild and then, wham, the soil has begun to warm up and you’re three weeks behind instantly. And that’s that.”

Lord Thurso’s vegetable patch is no normal allotment. Sheltered by Caithness stone flags from the dilapidated castle ruined by his great-great-grandfather’s modernisation plans, the patch is the size of a London suburban garden, overlooked by a few curious horses, which poke their noses over the hedge, puzzled by the camera flash of The Times’s photographer.

With the rows neatly and freshly hoed, one wonders whether Marion, his American wife who lives at the family home in Thurso all week, has been helping her Liberal Democrat husband ahead of our visit.

Still, armed with trowels, wellies and secateurs housed in an old outhouse stuffed with junk, the 55-year-old peers through the green netting covering his strawberries, which he spent hours erecting just the week before.

“I admit that it’s the rhubarb which is most embarrassing,” Lord Thurso says, eyeing the splayed, green and pink trifid in the middle of the patch.

It is not surprising that Lord Thurso turns to the quiet pursuit of tending sprouts, given the past 18 months in Parliament. Apart from the nuclear row over MPs’ expenses, a row that has left Lord Thurso unscathed, Parliament has been trying to grasp the consequences of a banking crisis, which brought the financial system within hours of collapse.

Lord Thurso is one of two Liberal Democrats who sit on what has become one of the most high-profile committees in the Commons, the Treasury Select Committee, which has the job of trying to make sense of the hundreds of billions of taxpayers’ money stuffed into the banking system to avert the collapse of a big lender.

He is also one of just a handful of the 14 MPs who sit on the committee with any real experience of the business world. That experience has been vital, as they grilled the likes of Sir Fred Goodwin, the former chief executive of Royal Bank of Scotland, Eric Daniels, the chief executive of Lloyds Banking Group, and Mervyn King, the Governor of the Bank of England, as part of their inquiry into the causes and consequences of the banking crisis.

Since the run on Northern Rock in September 2007, members of the Treasury Select Committee inadvertently became some of the most prominent backbenchers in Parliament, regularly shown on evening television news programmes, crossexamining the bankers and regulators who were widely blamed for the crisis.

Lord Thurso admits that constituents would approach him as he left church on Sundays, urging him to “sock it to them”.

Assuming the role of cross-examiner of the City’s wealthiest financiers is not one that would have been obvious to those who have known Lord Thurso of old. While it is Parliament that defines him now, for those who knew the viscount before his election in 2001, Lord Thurso is a caterer and a man whose life and family are steeped in the small harbour town just one stop away from the Orkney Islands.

On leaving Eton just before his eighteenth birthday, Lord Thurso worked as a ghilly and understalker to supplement his £40-a-month inherited stipend and £6-a-month salary. His first real job was at the Savoy hotel on the Strand from September 1972.

His real break did not come until he was offered the job of general manager of the Lancaster Hotel in Paris, also owned by the Savoy Group, when he was 27. “It was there that I taught myself how to manage, what motivates people and how you get a team to work.”

Lord Thurso’s interest in decent food seems to be derived from his career-long stint running some of the world’s poshest hotels. Recalling the Lancaster in Paris, which is just off the Champs Elysées, he says: “The French really do have an astonishingly different set of priorities. The staff insisted that their canteen was up to scratch; it served food that most restaurants in the UK would have been happy to serve. We’re talking quail and lentils. And if you suggested that you withdraw their glass of red at lunchtime, it would be death with the union.” Lord Thurso freely admits that when in London, he eats well at the likes of Mosimanns in Belgravia.

By the mid-1980s, Lord Thurso had developed a reputation as a trouble-shooter, turning around tired hotel chains and taking risks on new projects. In July 1985, he was approached by Blakely Hotels, which had just bought Cliveden, the stately home, infamous for hosting the first occasion when Christine Keeler met John Profumo, then the Secretary of State for War.

It was Lord Thurso who was charged with turning a National Trust property with a budget of £8 million into the most expensive hotel in Britain. Apart from visits from people such as Princess Diana, the hotel cashed in on the City boom and the new breed of yuppies keen to display their wealth. It was Lord Thurso, too, who turned around the failing Champneys health spa chain and only recently has he chosen to step down from Millennium & Copthorne, the international hotels group where he was deputy chairman. While it is understood that he quit over a corporate governance row he refused to be drawn on the group.

If Lord Thurso has built a career out of commercialising past splendour, it is in stark contrast to his own home in Caithness. While his family seat dates back to the 1600s, it was his great-great grandfather Sir Tollemache who, in the 1860s, built a grander pile on the same site, using timber that he had found washed up on the adjoining beach as joists for the new home. The materials and the design were unstable and the “modernisation” a disaster. By the 1950s, Lord Thurso’s parents decided to give up, remove the roof and move into the servants’ house next door. Lord Thurso was born in the bedroom he now shares with his wife. Lord Thurso’s vegetable patch is on the site of his father’s own once carefully tended garden and his mother lives in a bungalow only a few feet from his front door.

Sitting at home, surrounded by family photographs that remind any visitor of Lord Thurso’s impressive family connections (he and Marion hosting the Prince of Wales and Duchess of Cornwall; his grandfather standing next to Churchill, signed “Winston, 1916”), the Third Viscount is a long way from his other business obsession. As president of the Tourism Society for the UK, he is furious that the Government has failed to recognise properly an industry that makes up 7 per cent of the British economy and pulls in £79 billion a year. Despite employing 5 per cent of the British workforce, no Government department has the word “tourism” in its name.

“It’s not just the Treasury. The Cabinet don’t get it, either. Tourism has always been at the end of the food chain for them. The real spend for ‘Visit Britain’ [the national tourism agency] is either static or going down.”

For a man whose landmark hotel was synonymous with the Profumo scandal, one is tempted to cite Mandy Rice Davis when looking at Thurso’s grumbles about tourism: “Well, he would [say that], wouldn’t he?”

But Lord Thurso points out that Britain’s under-investment in holidaymakers places London at risk of being “under-bedded” (with too few hotel beds) for the Olympic Games in 2012. He adds that the Government could be drawing up plans to train London families to cater for homestays, where homeowners near the Olympics’ site could rent a room during the event.

It is the kind of idea, perhaps, that can only emerge when you have the time to think while tending the cabbages.

CV

Born 1953

Education Eton

Career Management trainee, Savoy Group, 1972; manager, Lancaster Hotel, Paris, 1981-85; founded Cliveden as hotel, 1985-92; chief executive, Granfel Holdings, 1992-95; chief executive, Champneys, 1995-2001; non-executive chairman, Walker Greenbank, until 2002; non-executive deputy chairman, Millennium & Copthorne Hotels, 2002-09

Politics Liberal Democrat MP for Caithness, Sutherland & Easter Ross since 2001