Some say that the unusual triangular shape of romantic Midford Castle, which dominates the village and valley of Midford, three miles from Bath, represents the Ace of Clubsa reference to a fortune winning card allegedly played at the gaming tables by Henry Disney Roebuck, who built the castle in 1775. This theory was discounted in Country Life (March 3 and 10, 1944) by Christopher Hussey, who suggested instead that Mr Roebuck was ‘a wealthy romantic (who) chose the plan and design of the building chiefly for aesthetic reasons’, based on contemporary plans by John Carter, a Gothic enthusiast who worked with James Wyatt, and was on friendly terms with Horace Walpole.

Whatever the origins of Midford Castle, now listed Grade I, its subsequent history is full of romantic twists and turns. In 1810, the castle was bought by one of the Conollys of Castletown in Co Kildare, who added the porch (said to give the Ace of Clubs its stalk) and built the nearby stables and chapel. The latter fell into disrepair after the last of the Conollys sold the house in 1901, since when the present owners, Mr and Mrs Michael Briggs, who bought Midford in 1961, have incorporated the chapel into the garden as a picturesque ruin.

During their 45 nyear tenure, Michael and Isabel Briggs have patiently restored and improved the castle, buying back its various dependencies as they became available, and adding much of the surrounding 59 acres of parkland, grassland and woodland to create this picturesque country estate on the outskirts of Georgian Bath.

‘The castle is nowhere near as big as it looks,’ says Mrs Briggs, for whom the renovation project of half a lifetime has been ‘a tremendous pleasure’. Yet, not only has this remarkable lady brought up three children while overseeing the renaissance of Midford, she has also produced a steady flow of bestsellers, as Isabel Colegate, including The Shooting Party, the ‘Orlando’ trilogy, The Summer of the Royal Visit, and most recently, Winter Journey. Her husband, Michael, has been no less involved, both at Midford and locally, as the long standing chairman of Bath Preservation Trust.

But now it is time to move on, and the Midford Castle estate is for sale through Humberts (01249 444555) at a guide price of £5 million. ‘This is Somerset’s biggest estate sale of the year so far, and not just in terms of price, but for the uniqueness of Midford’s setting, its extraordinary collection of historic buildings (the main three storey house has seven bedrooms and three reception rooms) and its accessibility from London by road, rail and air,’ says Christopher Jerram of Humberts.

A guide of £4.5m ranks the beautiful Willett estate at Lydeard St Lawrence, a short head behind Midford in terms of price, but although different in style, Willett is peerless in all other respects, says Brian Bishop of selling agents Jackson-Stops & Staff (01823 325144).

Deep in the heart of the estate, Grade II*-listed Willett House built for rich landowner Daniel Bloomart by Richard Carver in 1816 sits quietly in its 69-acre park, created in 1840, against the dramatic backdrop of the Quantock and Brendon Hills. This wonderfully unspoilt gem of a Georgian country house has four particularly fine reception rooms, master and guest suites, and four further bedrooms, as well as a five bedroom annexe, a cottage, a stable block and a heated indoor swimming pool. Willett also has its romantic ruin the intriguing Willett Tower built by the local gentry in 1782, perhaps as a steeple landmark for cross-country riders.

Later owners of the estate have included the Cadbury family, Mrs Suzanne Beadle, whose husband founded the British Field Sports Society (BFSS), and, since 1960, the indefatigable Rosemary Heys, who has used Willett House and its glorious lakeside gardens as a regular venue for charity balls and outdoor concerts.