Dunsborough Park: A home for sale next door to Wisley with gardens that look like they've been created by the RHS

How rare a find on the open market is a place like Dunsborough Park? We've been pondering this question for a few days now.

After all, you could spend months looking for an 18th century house which has been cared for and sympathetically extended by generations of different owners. You could spend years looking for an estate of 100+ acres within a stone's throw of the M25. And you could spend a lifetime looking for a place whose gardens are so unfeasibly magnificent that you can imagine members of the Royal Family seeing the pictures on this page, and then calling their gardener in to answer some awkward questions about why their own plots aren't in the same category.

Dunsborough Park's recorded history goes back to the 12th century, but the house on the current site was originally a 17th century farmhouse. Over the succeeding centuries – and particularly in the 19th century, when owned by the Onslow family – a vast amount has been added and modified, and modified and added.

So much has been added, in fact, that those original farmers would not recognise the home now on sale via Savills for £17 million any more than they'd be able to harness up one of the gleaming metal machines parked in the driveway and use it to plough their fields.

The eight-bedroom house itself has some magnificent, striking features within, particularly as regards the principal reception rooms.

There's a drawing room with floral silk and cotton wall covering, marble fireplace and full height windows; the dining room is just as grand, with its marble fireplace and hand-painted hessian wallpaper imported from Italy.

There are traditional features including exposed beams, while more modern touches include a conservatory. It's the newest of Dunsborough's additions, having been added by the current owners as a perfect spot from which to overlook the garden and parkland.

We can see why they added it with that in mind, for the garden and parkland in question are truly staggering. Dunsborough's borders run within yards of the borders of RHS Wisley, and from the looks of things you'd be forgiven for thinking that a naughty former owner somehow pinched a large chunk of the latter while the custodians of the Royal Horticultural Society's pride and joy were on holiday.

Dunsborough's gardens owe a great deal to Oliver Simmonds, an MP who bought the property in the 1930s. It was he who had the Tudor style gatehouse at the entrance built, as well as the octagonal pumphouse, the bridge, pavilion, greenhouses and ha-ha.

After the war, however, the gardens fell into decline until 1994 when the current owners, the Sweerts (or Baron Dolf and Baroness Caroline Sweerts de Landas Wyborgh, to give them their full titles) bought the place.

They brought in garden designer Penelope Hobhouse and landscaper Simon Johnson, and later another gardener in Rupert Golby, who over the years have made the gardens what they are today. Our gardens editor Kathryn Bradley-Hole visited in 2011, and wrote this afterwards:

The grounds now include a series of small intimate areas, dividing the garden into rooms and creating long vistas; there are water gardens, featuring a series of descending ponds leading to the Ockham Mill Stream, with the bottom pond crowned by a magnificent folly bridge. And there are hundreds of statues – as you'd expect, given that Dolf is a garden statutary dealer.

Both Baron Dolf and Baroness Caroline have been keen to open the gardens to the public, running open days both as part of the NGS scheme and of their own volition, including the annual Festival of Tulips in April.

Beyond those gardens, the estate contains far more: 10 further cottages, tennis courts, garages and at one end of the house there is a space referred to as the 'concert hall', complete with high ceiling and viewing gallery.

It's originally believed to have been built as a Fives court, but has also been an indoor swimming pool – the original foundations are still in place, should the new owner wish to return it to more sporting use.

And speaking of sporting pursuits, it's also a perfect property for horse lovers: among the outbuildings are excellent equestrian facilities, including 17 boxes, 2 foaling boxes, a manège and paddocks.

Paul Finnegan of Savills' Country House department is confident that a buyer will be found for what he describes as a "striking estate", citing in particular the range of top-quality educational establishments nearby. Dunsborough, he says, "is surrounded by some of the country’s top schools – essential criteria for the discerning family-focused grand country home owner."

As good as the location and house is, though, it's the grounds on offer which Mr Finnegan believes will be one of the key factors: "We expect interest from buyers who will be able to appreciate and preserve these beautiful grounds as well as being able to enjoy the fabulous equine facilities on offer."

Dunsborough Park is for sale via Savills, priced at £17 million – see more pictures and details.