Luke and Brian Comer
Rank 2017

The Comers' latest developments include Royal Connaught Park, a former Hertfordshire private school with a dining hall that was used in the first three Harry Potter films. The brothers, originally from Galway, are developing 380 luxury homes on the site in Bushey. They began as plasterers in 1971 and then built a British and German property portfolio. They own five stud farms and claim to have 500 companies worldwide, with assets of £2.25bn. We can see £91.2m of assets in their 14 British companies. Luke, 59, lives in Monaco while Brian, 57, has a home in Hertfordshire.