The most expensive home in Britain is believed to have been sold to a Russian billionaire for an estimated £140 million.
  There has been intense speculation over which oligarch could have bought Park Place, a 300-year-old country house set  in 200 acres of land in Oxfordshire.
   The mansion, which backs on to the Thames, has a helipad, spa complex, home cinema and  high-tech security system. 
  Once home to George II’s eldest son, the property has been given a makeover worth millions for its mystery new owner who is understood to have bought UK properties in the past.
  The record purchase beats the sale of a penthouse at One Hyde Park, Knightsbridge, for £136million earlier this year.