Spencer-Churchill’s own early memories of Blenheim are of playing outdoors on the lake designed by Capability Brown: “James and I had boats, and my father used to take us water- skiing on the lake. We had great fun at weekends as our friends came down and we had barbecues at the boathouse.” She and her brother always spent a lot of time together. “When you go through a tough childhood, in the sense that your parents divorce, you become very close. I did boyish things with him such as biking and go-karting. I had my own pony and rode a lot, but he wasn’t into riding.”

During the school holidays, Spencer-Churchill and her brother worked in the gift shops selling guidebooks and ice creams, and helped the head gardener, Mr Page, to pick vegetables and fruit.

The charm of Blenheim, she maintains, is that it remains a lived-in home. “The east wing is the private part, although some of it is open to the public at certain times of the year. People who come for the first time are amazed at how cosy it is. The rooms have big proportions, with high ceilings and large windows, but it is incredibly welcoming, with lots of family photographs and three rowdy golden retrievers and labradors that rule the roost.” The rest of the palace, primarily the south facade and west wing, is open to the public, attracting more than half a million visitors each year.

“Two of my favourite rooms are the Great Hall and the Saloon, but I equally love the finer decoration and plasterwork of some of the smaller rooms. It is difficult to have favourite paintings or furniture because every room has its own style and speaks for itself.”

For Spencer-Churchill, the rooftops are the best place to view the scale of the building, the gardens and lake. “There is no better vantage point to appreciate Blenheim than from the rooftops, because when you go up there you get this amazing perspective on the complexity of the building.”

She admires the work of all the architects who contributed to the building. “They all had something different to offer,” she points out. “Sir John Vanbrugh wasn’t a trained architect, he was a playwright, but he had some practice as he did Castle Howard before Blenheim. Nicholas Hawksmoor worked under Vanbrugh and then he came back and worked on his own after Vanbrugh was dismissed.”

Having grown up at Blenheim, it is hardly surprising that Spencer-Churchill decided to work in interiors, yet she maintains her aristocratic background was more a hindrance than a help. “An appreciation of architecture and art was drip-fed into me,” she says. “To be honest, it was more difficult being who I am. I think a lot of people thought ‘She doesn’t have to work’, but I wanted to be taken seriously, particularly by the trade, which is one reason why I set up the shop in Woodstock.” She has run Woodstock Designs, specialising in the renovation of country homes, for 25 years, and has a studio/office in Fulham, west London.

Her track record as an interior designer recently won her a plum new job: design consultant on the refurbishment of Easton Neston, the Grade I Jacobean pile in Northamptonshire that Lord Hesketh sold last year to Leon Max, the Russian-American clothing entrepreneur, for about £15m. One of Britain’s most important country homes, it needed someone with experience of grand houses — enter Spencer-Churchill, who is advising on architectural and design details, as well as decoration.

“At present we are waiting for planning approval for various aspects of the refurbishment,” she says. “We are all keen not to change the existing character of the house, and restoration will be kept to a minimum.” The Maxes “are happy for the house to evolve over a period of time”, she says.

She is so passionate about Blenheim, she spends most weekends at her farmhouse outside the park. “I absolutely adore Blenheim. I feel a certain amount of duty to help where I can, but it’s not a burden on me. My father is going to be 80 this year, and is still very active. There is a huge upkeep, and you never know what’s going to go wrong next. I’m a trustee of the charitable foundation and I help with any refurbishment.”

Her own children, David, 24, and Max, 21, from whose father, a German-born banker, she is divorced, will not inherit the place, but it has been a part of their life as well as hers. “My sons are not in the line of succession, but they’ve grown up with Blenheim as we’ve always had a house near there. George, 13, James’s son and my nephew, will be the next duke after James.”

For Spencer-Churchill, there is nothing like a weekend ride or stroll on the lands steeped in family history. “My therapy is getting out on my horse and riding around the beautiful park and walking with my dogs. I feel very privileged, but certainly don’t take it for granted.”

Blenheim and the Churchill Family: A Personal Portrait by Henrietta Spencer-Churchill is available at The Sunday Times Books First price of £27, with free UK p&p, on 0870 165 8585 or www.timesonline.co.uk/booksfirst

Woodstock Designs, 01993 811 887, www.wakeuptowoodstock.com

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