Marcus Cooper, the north London property developer, has won planning permission to redevelop the buildings, designed by the Regency architect John Nash, when Cancer Research, the current occupiers, move to new offices in April.

 

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Marcus Cooper bought the buildings at 6-10 Cambridge Terrace and 1-2 Chester Gate for £23.7m in 2007, but hopes to sell the completed “super-prime” residence for £100m.

 

The plans include 10 huge bedroom suites, several vast reception rooms and a basement leisure complex including a cinema, gym and swimming pool.

A 40-ft roof garden, complete with a sliding ceiling and overlooking Regent’s Park, will be built into the eaves, and the development will come with two additional staff houses.

 

The “mega-mansion”, which will be sold to a single owner, will claim the title of London’s biggest residence after Buckingham Palace – an accolade currently held by Witanhurst House in Highgate.

 

If sold for more than £100 million, the Regent's Park development would also claim the title of London’s most expensive home.

 

The official record was set in February 2008 when a buyer paid £80 million for a detached house in Kensington’s Upper Phillimore Gardens.

Camden Council approved Mr Cooper's plans on the condition that affordable housing is built on another site.