Lotherton was not the family's main seat. That was Parlington Hall, a few miles away - a grand country house that the Gascoignes had occupied since the seventeenth century. Lotherton was a smaller manor house that came into the family in 1825 when Richard Oliver Gascoigne bought it. In 1842 both his sons died, leaving the estates to his unmarried daughters Elizabeth and Mary Isabella. The sisters divided the family lands; Mary Isabella took Parlington, Elizabeth took Lotherton. Through Elizabeth's marriage to the 2nd Baron Ashtown, Lotherton was mostly let to tenants between 1842 and 1893. It is only with Colonel Frederick Gascoigne, who inherited Lotherton in 1893, that the house began to be transformed into the country residence we see now.

Colonel Gascoigne's wife Gwendolen was the daughter of the engineer Sir Douglas Galton, and the second cousin and goddaughter of Florence Nightingale. She brought to Lotherton both a strong design sensibility and a deep family connection to one of the most famous Victorians. Between 1896 and 1931 the Gascoignes remodelled the house extensively for their growing family - adding a dining room, an entrance hall, a drawing room and a servant's wing in the comfortable Edwardian country-house manner. Gwendolen designed and built the formal Edwardian gardens that still run along the south front. When Parlington Hall began to fail, the Colonel moved furnishings across to Lotherton; the Gascoignes essentially transferred the family's domestic centre from one estate to the other. Parlington was demolished in the 1950s. Lotherton inherited its contents.

Sir Alvary Gascoigne, the Colonel's son, was a career diplomat - British ambassador to Japan, then to the Soviet Union. He inherited Lotherton in 1937. The house filled with Oriental works of art he had collected during his postings. His first marriage to Sylvia Wilder produced one son, Douglas, who joined the army during the Second World War and was killed in his tank in Normandy on 6 August 1944. The Gascoigne line ended there. Sir Alvary's second wife Lorna lived with him at Lotherton until his death in 1970, but there were no further children. In 1968 he made the gift: house, grounds, contents, and an endowment for future acquisitions, all to the City of Leeds, opened on the August anniversary of his son's death.

What Leeds inherited was extraordinary. The Lotherton collection runs to about 3,000 objects across five categories. The headline piece is Pompeo Batoni's 1779 portrait of Sir Thomas Gascoigne, painted in Rome during the Grand Tour - Sir Thomas posed as a connoisseur among books and sculptures, holding a snuffbox that bears the portrait of Marie Antoinette. The actual snuffbox is also in the collection, one of those rare cases where the prop and the painting survive together. There are five Joaquin Sorolla beach paintings from 1906. Four George Clausen portraits and three of his landscapes. Furniture by Pugin, Burges, Charles Rennie Mackintosh, William Morris, Voysey, Webb and Godwin - essentially a textbook of nineteenth-century English design under one roof. The studio pottery collection includes Bernard Leach, Hans Coper and Lucy Rie.

The estate is more than a museum. Red deer graze the parkland. The bird garden holds endangered species in a programme established in the 1960s; in 2003 a walk-through aviary called "Into Africa" was added. The twelfth-century Norman chapel in the grounds - used as a place of worship for the lost medieval village of Lotherton, then restored during the First World War to house wounded soldiers under the V.A.D. hospital scheme - still stands. Every winter the estate runs the Lotherton Christmas Experience, which had 64,743 visitors in its first year (2016) and has become one of the largest seasonal events in the north of England. For a country house that was never the Gascoignes' first choice, Lotherton has become a busier and better-loved place than Parlington, the family seat, ever was.