The Duke of Marlborough obituary

Blenheim Palace, in Oxfordshire, has a romantic history: it was the reward for the first duke of Marlborough's 1704 victory over the French at the German village of Blenheim. The palace is also famed as the birthplace, in 1874, of Winston Churchill. But unfortunately for the 11th duke, John Spencer-Churchill, who has died aged 88, in the 20th century the care of stately homes had to become a business, or else they would crumble. The duke found that, while he revered his ancestors and loved Blenheim Palace and its estate, the running of the place became the family's biggest challenge.

Central to the duke's concerns was always the care of Blenheim. The vast baroque house and its estate – designed by Sir John Vanbrugh and landscaped by Capability Brown – was, by the 1980s, costing the family more than £100,000 a year just to heat and light. The duke maintained that without substantial profits from the estate, good management and efficient marketing, the house would be unviable because public admission fees covered only basic maintenance, not restoration work. Through astute management, he managed to increase turnover from £2m a year in the 1980s to £10m by the 1990s.

Usually the duke kept well clear of visitors, though he was invariably courteous when confronted. His nickname, Sunny Marlborough, did not allude to his personality but to his childhood courtesy title, the Earl of Sunderland. Son of John, the 10th duke, and his wife, Mary (nee Cadogan), he was educated at Eton. He spent seven years in the army, in the ranks and then as a captain in the Life Guards. He inherited the title, the palace and 11,000 acres in 1972 on the death of his father.

Beyond his devotion to Blenheim was his concern for the countryside as a whole. He was one of the first to point out that countryside interests had become far less fashionable than those of towns and cities. When, in 2000, he welcomed the minister of agriculture, Nick Brown, to Blenheim for a conference of the European Friends of the Countryside, he asked the government to recognise that farmers and landowners had less scope than others to diversify into other businesses. However, he was successful at diversification himself, establishing a bottled water plant and selling wooden garden furniture from Blenheim. The park – a world heritage site – is now a venue for events from jazz concerts and antiques fairs to jousting tournaments, and has been the subject of TV series including The Aristocrats (2012) and Great War House, the recent documentary presented by Julian Fellowes.

The duke also served as chairman of the drinks company Martini & Rossi, and president of the Thames and Chilterns Tourist Board, the Oxfordshire Association for Young People, the Sports Aid Foundation for the southern area and Oxford United football club. He was a deputy president of the National Association of Boys' Clubs, honorary president of the Football Association, a council member of the Winston Churchill Memorial Trust, and patron of the Oxford branch of the Red Cross.

But it was Blenheim that dominated his life. He acknowledged that he was shy with people and that he tried to run the estate as if it were a regiment with himself as commanding officer.

He is survived by his fourth wife, Lily Mahtani, whom he married in 2008; by the son, Jamie, and daughter, Henrietta, from his first marriage, to Susan Hornby, which ended in divorce; and by a son, Edward, and daughter, Alexandra, from his third marriage, to Rosita Douglas, which ended in divorce. Two sons predeceased him.

His heir, Jamie, Marquess of Blandford, was once a drug addict who served three prison terms. In 1993, while the marquess was in a drug rehabilitation clinic, the duke began a legal action to prevent him from inheriting Blenheim. In 1994, following complex litigation, the duke was successful in establishing a trust that would put the trustees, rather than Jamie – by then on probation for theft and forgery – in control of the estate, while granting the marquess the title and a life interest.