He was 22 when he took over running the castle with his mother, becoming sole custodian after her death in 1999. He moved to a nearby farm in 2001 but the castle is still a home with 12 lived-in apartments. It is also a tourist attraction receiving 160,000 visitors a year, as well as a wedding venue.

Maintenance is a full-time job for a team of five and, “much like the Forth Bridge”, work will never be finished. But Mr Watson-Armstrong is keen to keep the castle in his family. “I’m determined to never let it fall into public body hands,” he says.

“It costs hundreds of thousands of pounds a year to maintain and run it, but I would rather meddle in the affairs of the castle myself than have someone who has not lived there, or does not know it, in charge.” His son William, 29, is taking on more responsibility for the castle with the hope of increasing visitor numbers and improving the experience.

Jodrell Bank Observatory, which has played a leading role in astronomical research since 1945, has been added to the Unesco World Heritage List.

The site in Cheshire has contributed to the study of meteors and the moon, the discovery of quasars, quantum optics, and the tracking of spacecraft.

It is probably best known for the landmark Lovell Telescope, a steerable 250ft radio dish which was the largest in the world when it was built in 1957.

Weighing 3,200 tonnes, it can be seen for miles around, it is still the third-largest of its kind and has appeared in Doctor Who and Douglas Adams’ Hitchhiker’s Guide to the Galaxy.

Jodrell Bank, which is part of the University of Manchester, joins historic international sites such as Machu Picchu, the Great Wall of China and the Taj Mahal on the Unesco world heritage list.

Announcing the decision, Unesco said: “Located in a rural area of northwest England, free from radio interference, Jodrell Bank is one of the world’s leading radio astronomy observatories. This exceptional technological ensemble illustrates the transition from traditional optical astronomy to radio astronomy (1940s to 1960s), which led to radical changes in the understanding of the universe.”

The public body responsible for looking after some of England’s most historic places has issued a stern warning to people who indulge the art of stone stacking in protected spots.

Historic England said that in some circumstances people who balance or stack stones may be breaking the law and could even face jail.

Stacking or balancing stones is a pleasing pastime for some lovers of the outdoors and a precarious natural sculpture is a familiar sight on mountain, riverside and beach.

But Historic England said stone stackers should not tamper with spots classified as ancient monuments.

The warning followed concern that stone stacking was putting the neolithic site Stowe’s Pound on Stowe’s Hill in Cornwall at risk.

Caradon Archaeology posted images of “fairy castles” – stone stacks – on its Facebook page and called for the registration plates of anyone seen piling stones to be taken and reported.

The post said: “Stowe’s Hill is a 6,000-year-old settlement, built by our neolithic forebears. It is a protected, scheduled monument.

“This practice is not only vandalism; it is illegal, and carries with it a possible prison sentence. If anyone sees anyone attempting to move stones please warn them of this and message us. Or try and get their registration number and message it to us.”