Mary-Anne Robb hurls the Range Rover over bumpy Somerset lanes at an alarming pace, apologising only for driving slowly. She has some newly repaired ancient plates stowed in the back and she doesn’t want them to break.

“This part of England hasn’t changed in hundreds of years,” she announces, braking abruptly to reveal, across a mirror of water, the medieval gatehouse of Cothay Manor, her home for the past 15 years, standing serene in its own time warp. A visit to Cothay is like turning back the clock, even before you smell the beeswax or spot the wingless angels on the huge trusses of the Great Hall.

They don’t do wow factor like this any more, but then you don’t meet women like Mary-Anne very often, either. An old-school eccentric who is usually accompanied by three pekinese - Truly Scrumptious, Yum Yum and Darling Boy - she won’t discuss her age, saying simply that she is “old”, but such is her enthusiasm and energy that in many ways she’s more like a young girl than the formidable chatelaine of what the historian Christopher Hussey has called “the most perfect small 15th-century country house in England”.

At Cothay, a five-bedroom manor house near Wellington, Mary-Anne is responsible for the award-winning romantic garden; her husband, Alastair, concentrates on structure and proportion. Inside, her talent and passion are evident throughout, from the curtain fabrics, faithfully copied from originals in museums, to the upholstery and wood finishes, which she did herself, thanks to evening classes. The house is filled with collections of everything from early embroidery to Viennese cold-painted bronze insects, medieval objects and Chinese porcelain.

“We had no capital, because I am the third of five sons,” Alastair says. “To get the sort of house we wanted, we had to buy things other people didn’t want and do them up. This is the fourth house we’ve renovated. Mary-Anne has been an absolute brick. Not many wives would live on a building site all their married life.”

It is of just such gloriously British eccentricities and beautiful country houses that television programmes are made. The Robbs, serial renovators, are the first participants in a new series on Channel 4, Country House Rescue. It throws open the doors to six stately homes in Surrey, Gloucestershire, Somerset, Cornwall, Ayrshire and the Scottish Borders, revealing these houses in their full glory. It also introduces us to their respective owners and gives an idea of the challenges they face.

Ruth Watson, the uncompromising businesswoman, troubleshooter and former presenter of The Hotel Inspector, will tell the owners how to diversify and raise cash to keep their expensive roofs over their heads. Predictably, her advice ruffles a few stately feathers.

The Robbs are outspoken and proud of it, and when Mary-Anne speaks in her clipped patrician voice of stopping “to fill up with gas”, the Americanism jars. It turns out she has had her car converted to save money - when she says gas, she means gas. The heating at Cothay, too, is powered by wood chips - impressive, until you realise that this is a woman who will save money by taking an £8 coach trip to London rather than the train, only to buy a costly 16th-century painting when she gets there.

Not that this gives her any brownie points with Watson. The Robbs, who have four grown-up children and nine grandchildren, open their house to groups of more than 20, getting 90-100 such groups a year, as well as 5,000 or 6,000 visitors to the garden in summer. Yet they are struggling to make the house pay its way.

“Simon Jenkins gave Cothay four stars in his England’s Thousand Best Houses - one below Chatsworth - and said that few houses in England remain so evocatively medieval,” Mary-Anne says. “But we have never made a profit. We never take holidays, though I’ve been on botanical expeditions to China and South Africa. People ask what I do in the winter, but it takes a month just to rake the leaves and several months to prune.”

The house is best known for its 12-acre garden, laid out in the 1920s and since replanted by Mary-Anne within the original framework of yew hedges. She also single-handedly got the Ministry of Defence to place an exclusion zone for its helicopters over her house, and was adamant that, although they “could do with some help to restore the wall paintings”, they didn’t need rescuing.

Restoring a house is one thing, but keeping it is quite another, and it is this that has proved most challenging. So, how will Mary-Anne react to being told how to run things by a bossy woman with less taste but more commercial nous than herself?

She is circumspect about Watson and her methods. “She was provocative, but in the end we became firm friends,” she says. “She turned up and started telling us that we were extremely unsuccessful, and that the only thing that matters was getting a tearoom and shop. We called her Ruthless Ruth and learnt to say yes to everything she said.”

Watson suggested a calendar of events, so they are planning gardening and antiques courses; she called their website dull, “though we hadn’t had any complaints”; and she wanted to see the lavatories and plant shop nearer the tearoom. She was even rude about the jam the Robbs served. “Food was uppermost in her mind,” Mary-Anne says, “but what she doesn’t understand is that if you buy homemade jam, it is hideously expensive and runs off the scones.”

Watson goes for the financial jugular. “I don’t think it’s possible to run these places in an amateurish way,” she says. “You need cash flow. Whatever estimate you are given for doing up a country house, multiply it by 10. Builders will think you’re as rich as Croesus. And the overheads are always going to be more than on a terraced house.

“The lesson is, if you’ve got £2m, buy a house for £1m and keep the other £1m. Don’t spend it all and think that, by running it as an attraction, you’re going to make money. You shouldn’t buy one of these places if you don’t have working capital.”

Sadly, such simple economic advice doesn’t help when you inherit a run-down old stately, which was the fate of Anselm Guise, a 36-year-old dance DJ, whose uncle left him Elmore Court, in Gloucestershire. The £25m estate has been in the Guise family for nearly 800 years, but in the 21st century, the 18-bedroom, Grade II-listed mansion is crumbling. Watson shows up with her uncompromising, often acerbic wisdom. She has a lot of work to do.

The owners of Albury Park - one of Surrey’s most important country houses, with 63 individually designed chimneys – are £4m in debt and share their home with a number of elderly residents, shelling out for 21 staff and a heating bill in the tens of thousands. Then there is Chesters, a Grade A-listed Georgian home in the Scottish Borders, inherited by John Henderson, who works in advertising and lives with his wife, Ellie, an actress, in London.

You’ll have to watch the programme to see how they fared - but did Watson’s frank advice work for the Robbs? “We’ll do anything to help the home economy,” says Mary-Anne, who, encouraged by Watson, is now upgrading the tearoom. “Ruthless Ruth wants us to open earlier and do lunch. She said to keep it simple and to serve a sort of sandwich called a ‘banini’.”

Country House Rescue will start on December 9 on Channel 4; www.cothaymanor.co.uk

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