£35million knockdown project: Mayfair mansion marked for demolition, planning permission for £65million home House is liveable but earmarked for demolition Developer will have to pay £35million before calling the builders They could still stand to make between £20 and £28million A house in London is expected to become Britain's most expensive demolition project, costing £35million before the builders have even been called. But whoever is brave enough to take the project on could still walk away with a huge profit as planning permission has already been granted for a 16,000 square foot mansion. The five-storey property would feature an external guest villa and could sell for £65million, giving the developers a profit of between £20 and £28million. Grand design: the former coach house (left) has been granted planning permission to be turned into a £65million mansion complete with bowling alley (artist's impression, right) Estate agents say it will be the most expensive house demolition project ever undertaken in Britain. The new build would contain grand entertaining rooms including an entrance lobby, library, three reception rooms, family kitchen/breakfast room and 26-seat formal dining room. First floor plans show a 2,000sqft master bedroom suite, with walk-in dressing room, shoe room and two ensuite bathrooms as well as a further five bedroom suites on the two uppermost floors. As well as this the new mansion would provide a whole host of entertainment opportunities including a bowling alley, swimming pool and a cocktail bar/club-lounge. Peter Wetherell, Managing Director of Wetherell, who are selling the property said: 'The site is for sale for £35 million with consent to knock down and replace the exiting property. The extensive gardens will have a guest villa built in them (left) and will be in a highly desirable location (right) The new house will include a 2,000sqft master bedroom with walk-in dressing room, shoe room and two en-suite bathrooms Therefore some have called this site the most expensive house knock down in the UK. The planning allows the buyer to create a bespoke new mansion of outstanding luxury and quality with the completed residence worth circa £65 million, effectively doubling the value of site. For a discerning buyer this is an outstanding investment opportunity with the potential for huge capital value uplift. Mount Row, where the property is located, was originally occupied by stable yards and cabinet-making and upholstery workshops which served Mayfair's grandest mansions. The house was originally a carriage house built to accommodate horse-drawn carriages - with the coachmen sleeping in the eaves. Number 18 Carlton House Terrace is London's most expensive home, rumoured to be on the private market for £250million If the property sells for £65million it will smash the average asking price for W1K, the London postcode where it sits, which is £5.5million. However, it will fall well short of the most expensive home currently on estate agents' books which is a six-bedroom home in South Kensington, on the market at £105million. Another house, 18 Carlton House Terrace in St James', one of London's biggest homes, is rumoured to be on sale privately for £250million.