When I was doing work we did work for lots of the Russians and Arabs all around Knightsbridge and the West End. Obviously you never met the owners , you just met their PA , team of designers and main buildings Contractor.
These were beautiful houses over 4 or 5 or 6 floors , 18-20 bedrooms , fully re-wired , fully re-plumbed , top of the range bathrooms , en-suites all the bells and whistles. Just sat empty.
I would sometimes get sent back months after the job was complete to change a lamp and a security guard would let you in and see you out , not a sole living there.
My best guess is its some form of money hiding money. These places would be worth ÂŁ150million on the open market today