Jewellery worth more than £100,000 was stolen during a raid at the home of the elderly founder of Barratt Homes, police said today.
The haul, which included ruby and diamond necklaces, bracelets and earrings, was stolen from the mansion of Sir Lawrie Barratt on Monday night.
Masked men broke into the huge detached property, which is in its own grounds in Corbridge, Northumberland, while Sir Lawrie and one other person were inside.
Officers investigating the burglary believe the items were stolen for the purpose of being sold and are asking the public to contact them if they are offered jewellery to buy.
Northumbria Police have refused to identify the victims of the burglary.
But villagers confirmed that the property tycoon, whose granddaughter is married to Newcastle United defender Sol Campbell, was the target of the three raiders, who had Scottish accents.
One neighbour said: "It's the talk of the village. Everybody hopes he is all right, because he is a lovely older gentleman.
"There has been a lot of police activity, with officers coming door-to-door along Main Street. They wouldn't say what exactly happened but called it a serious incident."
Sir Lawrie made a fortune after founding Barratt Developments in the 1950s, which became one of the country's largest housebuilders. He is now retired and in his 80s.
Another local was surprised the criminals managed to get past the high security.
"The place is surrounded by cameras," he said. "It was hard enough getting in to collect conkers when we were little."
Detective Chief Inspector Paul Young said: "Three men were involved with this incident. They were wearing dark clothing and we believe they had their faces covered.
"They would have had to get through the garden to gain entry to the property so we believe they may have had torches and possibly a vehicle.
"This was a distressing incident for the occupants. There were two people in the house at the time but thankfully they were not hurt.
"I would continue to appeal to anyone who saw or heard anything suspicious to come forward."
Mr Young stressed that incidents of this nature are not common in Corbridge and elsewhere in Northumberland, and said residents should be assured that extra patrols are operating in the community.
Anyone with any information is asked to call police on 03456 043 043 or Crimestoppers anonymously on 0800 555 111.