A fine equestrian and agricultural estate on the edge of Clonmel, in County Tipperary, owned by the same family since 1797, is to be offered for sale on the international market.

Ballingarrane House, an 18th-century mansion on 280 acres, is being sold by the former Irish Olympic three-day event rider, John Watson, and his wife Julia.

Robert Ganly of Ganly Walters is quoting a guide price of over £3.5 million for the property but given that much of the land has undoubted development potential - it is within a mile of the town and has over two miles of road frontage - it will be no surprise if it makes considerably more when sold by private treaty.

The estate is also being marketed by Bill Montgomery of Sotheby's International Realty and CKD Kennedy MacPherson in London.

Mr Watson plans to dispose of his extensive dairy herd once a buyer has been found for Ballingarrane. He and his family will then move to a smaller farm where they will concentrate on training event horses. He has been at the forefront of eventing in Ireland over the last 25 years and was second in the world championship in Kentucky in 1978.

Ballingarrane is thought to have been designed by Sir Richard Morrison, who lived in Clonmel at the time, and who was subsequently responsible for the Regency mansion on Fota Island and Ballyheigue Castle near Tralee.

The Clonmel house was built by Solomon Watson, a cousin of John Watson of Ballydarton, who is reputed to have hunted and killed the last Irish wolf at Baltinglass in 1786. It is two storeys over basement to the front and three storeys to the rear with a range of rooms showing signs of having been a comfortable family home. From the moment one walks up the flight of steps into a large welcoming hall, there is nothing intimidatingly formal or particularly lavish about the decor or general order.

If anything, the house is all the more charming for being a little dated in some of its decoration and fittings. The exception is the front windows, which unfortunately were replaced some years ago with modern PVC. Several of the rooms have exceptional appeal. The diningroom and drawingroom are particularly elegant with tall windows overlooking the rolling acres and, in the distance, the Knockmealdown mountains to the west and the Comeragh and Slievenamon mountains to the east.

The diningroom has an attractive six-foot high black marble chimneypiece, which probably came out of an earlier 18th century house, as did another black marble fireplace in one of the bedrooms.

The Watson family spend much of their leisure time in a comfortable livingroom on the first floor return, which is lined with bookshelves and heated by a solid fuel stove.

The kitchen, two steps down from the diningroom, is large and atmospheric with a great pine table in the centre and a conventional Aga which keeps the place cosy day and night. Off the kitchen there is an office on one side and a utility room on the other, leading into a staff flat.

Upstairs, on the first floor landing, there is a handsome fanlight with ornate plaster work supported by superimposed Corinthian fluted pilasters. There are six bedrooms in all and three bathrooms. The main bedroom comes with an en suite bathroom and lovely views over the estate towards Clonmel. There are four acres of mature gardens running back from one side of the house - impeccable lawns, colourful herbaceous borders and shrubbery and a range of ancient trees. One of the entrances to the garden is through a cut-stone door-case of a demolished period house in Clonmel, which was rescued by John Watson's late father, Colonel Sidney Watson, the historical biographer.

A long curving avenue runs through woodlands and parkland to the main house, which has five bays and an elegant door case with baseless pediment and Doric columns.

The estate includes an attractive four-bedroomed house built in 1982, a steward's house and a farm cottage. There is a range of buildings at the rear which could easily be converted into additional accommodation. Separately, there is a stable-yard, a modern farmyard and a milking yard designed for easy management.

Clonmel is a thriving provincial town with a population of over 20,000. It is 56 miles from Cork and 104 miles from Dublin.