Anyone who has recently driven the back way to Henley from Oxford can hardly have failed to notice that those beautiful and mysterious gate piers framing a grand entrance to nowhere, just the other side of Stadhampton, have been sensitively restored. For many years they were somehow the very personification of picturesque decay, monuments to vanished vanities; now the late 17th- or perhaps early 18th-century pillars have had the stone balls, which originally crowned them, replaced . . . and thereby hangs a tale.

John Sykes, the chairman of the Oxfordshire Buildings Trust, has now sieved and collated information gathered during excavations, (financed by the Trust) that were undertaken a couple of years ago to try to finally unravel the mystery of the grand mansion that once stood beyond those gates.

It has long been known that William Dormer, known as The Splendid – because of such flamboyant foibles as having his horses’ hooves shod with shoes made of real silver, and having the insides of the wheels of his carriages made of the same metal – built a house called Ascott Park on the site in 1662, but that it burned to the ground before his family could move into it.

But various mysteries have long puzzled local historians: where exactly was the house he built, and where did the Dormers, ancestors of the Cottrell Dormers of Rousham, live before and after the conflagration?

The Dormers moved to Ascott, as the site is called (after a vanished medieval village there), from West Wycombe in 1518, and the estate stayed in their hands until 1760. Mr Sykes told me: “Our dig has revealed a later, failed attempt to build another house. This is indicated on an estate plan commissioned by John Dormer. We have dated this plan to between 1712 and 1727. It is likely the gardens and the tree avenue were laid out at the same time.”

He added: “The most likely explanation for abandoning work on the second house were debts incurred by John Dormer. His widow had to sell property after his death to repay loans. So it seems the Dormers never moved out of the old manor house they had first occupied in 1518.”

This original house, much reduced in size, remains on the site to this day, along with a dovecote and a building that may once have been a granary or an ice house. A chapel, once the parish church of Ascott and later the Dormers’ private place of worship, was demolished in the early 19th century.

As for John, grandson of the Splendid William, he appears to have been a blister of the first water, a rake whose misdeeds echoed down the ages.

For instance, according to Oxford historian Thomas Hearne (1678-1735), this “young gentleman of a most wicked, profligate, debauched life, a person of no conscience or religion, who is not known to have ever done one virtuous or good thing” once murdered a man in Woodstock Park (now Blenheim) for refusing to hand over his wife for him to ravish!

An ornate 17th-century gate (not the one that stood between the restored piers on the B480) existed in a decrepit state at the site well into the 20th century. It was given to the Victoria and Albert Museum, which has it in store, though not on display.

The county council acquired Ascott shortly after the First World War under a scheme to provide Homes for Heroes in the shape of small agricultural holdings for returning soldiers. After the Second World War much of the estate was sold to tenants, but the site of the manor was retained. The county council plans to open a visitor trail of Ascott later this year.