For most of its 700-year existence, Wall Hall in Aldenham near Radlett, Hertfordshire, was the very model of an English country gentleman’s residence, complete with Humphry Repton-designed parkland and a pedigree dating back to 13th-century landowner Guy de Walehale.

But during the second world war, Wall Hall became the playground of two of America’s most illustrious figures: banker J P Morgan, who owned it, and Joseph P Kennedy, United States ambassador to Great Britain and a Morgan house guest. After Morgan’s death in 1943, the estate was acquired by the county council and was given over to what later became the University of Hertfordshire. Now, property developer Octagon is building flats and houses on the site.

A pile with romantic ruins on more than 300 acres, Wall Hall is not quite what it seems. The castle-like facade was added in the early 1800s by then owner George Thellusson, who sold it in 1812 for £30,000. The new owner, Charles M Pole, added even more kitsch, scattering phoney ruins in the grounds. He also renamed it Aldenham Abbey.

Known as Jack, to distinguish him from his financier father of the same name, John Pierpont Morgan Jr bought the house in 1910. Although Morgan intended to be in residence only a few weeks each year during the shooting season, he furnished it lavishly, filling the conservatory with tropical plants and the chapel-like library with rare books (the Morgan Library in Manhattan houses one of the world’s most valuable book collections). He also purchased adjacent parcels of land until Wall Hall — he restored its name — totalled some 1,000 acres and encompassed several successful farms.

Morgan’s visits to the house were sporadic until 1936, when he had a heart attack. For the next seven years — until a fatal attack in Florida in 1943 — he spent more time there, entertaining the likes of King George VI and Queen Elizabeth. After the Blitz, Morgan put Wall Hall at the disposal of the royal family, urging them to take refuge there whenever and for as long as they wanted. This offer was never taken up — just as well, perhaps, as Luftwaffe bombers returning to Germany often deposited their spare bombs over Hertfordshire.

The illustrious owner and his royal guests are remembered in Aldenham, where locals still relate tales of a chance meeting with Morgan, or an act of kindness — a tip of a pound, a considerable sum in those days — from Mrs Morgan for some trivial errand. Virtually everybody in Aldenham worked for Morgan, and he is remembered as a paternalistic employer who insisted on the best, from furniture for his house to farm equipment.

For a controversial two years between 1938 and 1940, Joe Kennedy, father of future president John F Kennedy, served as America’s ambassador to the Court of St James. The Kennedy family — Joe, his wife Rose, and seven of their nine children (Joe Jr and JFK were at Harvard) — were ensconced in the ambassador’s official residence in Princes Gate in central London, in the 36-room mansion that had been given to the American government by Morgan.

With the outbreak of war in 1939, Morgan returned to America, and the hall was loaned to Kennedy, who stayed there at weekends. Locals remember seeing the children there sometimes, but it seems likely that Kennedy, an inveterate womaniser, also used the country house for romantic trysts.

“Joseph Kennedy was a showman who made a great hit when he arrived in London with all his young children,” says Michael Dobbs, author of Winston’s War and Churchill’s Hour. “He called them his hostages to show his bona fides in wartime. But as soon as bombs started falling, he left London, usually in the company of a young actress.”

Protected by its Grade II listing, the gothic mansion at Wall Hall is now being converted into flats, and new cottages and houses will occupy a 55-acre plot in the surrounding parkland. Currently for sale are three- bedroom cottages and semi-detached houses priced from £650,000. Later on, the development will include four- and five-bedroom houses, one-bedroom cottages, courtyard mews houses and flats, the latter in rooms which, if they had any ghosts, might be that of a king, a banker or the father of an American president at play.

Octagon, 01923 850 680, www.octdev.co.uk; Real Estates, 020 8446 5615

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