At about the same time, Craven commissioned Captain William Winde, who drew heavily on his Dutch upbringing for inspiration, to build Ashdown as both a hunting lodge and a retreat from the plague-ridden capital. Tragically, Elizabeth died in 1662 before she ever saw the house.

She bequeathed Craven all her papers and pictures — including many of the portraits that come with the property — as well as her collection of stag antlers, which she brought back from Bohemia. William lived another 35 years, but never married. Her bequest served as a daily reminder of his devotion.

The house then passed to Thomas Craven, the grandson of his first cousin, who did little but use it as a base to enjoy his passion for horses and hunting. A few alterations were undertaken in the 19th century, but the building remained intact until it was requisitioned during the second world war and occupied by the army.

It was left in a near derelict state until 1956, when Cornelia, countess of Craven, gave it to the trust. The organisation carried out some basic repairs, then let it out before the current owners bought it.

This is not an ordinary house, nor an ordinary sale. Anyone taking on the property, which costs an estimated £100,000 a year to run, must let members of the public, accompanied by a National Trust guide, view the house. It isn’t as onerous as it sounds — they are only allowed to visit the staircase and roof of the house on Wednesday and Saturday afternoons from April to October. The other rooms can be locked, and you need never meet the paying visitors.

Anyone expressing interest will be vetted by the estate agents: the current lessees are concerned that their vision for the house be respected. They will also be interviewed by the trust, which has a say in who takes on the property. When Ashdown last became available 25 years ago, there were 1,000 calls, 100 viewings and 30 offers; three prospective buyers were interviewed.

So, is this a good deal? “It is a trophy weekend house,” says Bruce Tolmie-Thomson, a partner in the country department of Knight Frank, which is jointly marketing the property. But wouldn’t you be better off stumping up the £12m it would cost to buy an equivalent freehold house — or renting one for an estimated £120,000 or so a year?

There are different ways of looking at the sums, but Tolmie-Thomson says buying the house for less than half that — albeit on a lease — could be more advantageous. “It frees up capital to invest elsewhere,” he says. “Financially, it’s the same as renting somewhere, but you pay up front.” Sam Butler, a senior partner at Butler Sherborn and an expert witness in valuation cases, agrees that it is a hard house to value. “If you extended the lease now, you might see some profit in the future,” he says.

That said, you would still have to furnish the place, which could add several hundreds of thousands — if not millions — to the cost. A dozen or so paintings, two obelisks and two urns are included, but the floor-to-ceiling bookcases, sofas, four-poster beds, full-length silk-brocade curtains, writing desks with postcard portraits of the Winter Queen on display and even the fitted carpets will have to be negotiated separately.

As will the retention of Maurice and his wife, who are full of the wisdom of the house. One of their most important roles is making sure tour groups don’t stray. “There’s a portable toilet round the back now,” Maurice says. “Nobody has ever used the loo in the house.”

- Ashdown House is for sale with Knight Frank (020 7629 8171, knightfrank.com) and Carter Jonas (01635 263000, carterjonas.co.uk)

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