Historic landmark Admiralty Arch is being turned into a luxury hotel after the government agreed to lease it out for £60m.
The ceremonial gateway between The Mall and Trafalgar Square, which was built as a memorial to Queen Victoria, has been leased for 99 years to development company Prime Investors Capital (PIC).
It wants to transform the building into a five star 100-bedroom hotel complete with royal and presidential suites, a ballroom, spa and fine dining restaurant.
Residential apartments are also planned for the first and second floors on the north side of the arch.
The deal is dependent on Westminster City Council granting planning permission for the multi-million pound conversion of the Grade I listed building.
Developers said the cost of the overhaul would be determined by what plans the local authority would consent to and admitted they did not have a “concrete time” for when they hoped to open the doors to the public.
Cabinet minister Francis Maude insisted the government had secured a “good price” for the building and dismissed claims it would become the preserve of the super rich.
“It is not the preserve of anyone at the moment and it won’t be,” he said.
“The bars and restaurants will be open to the public.”
He added: “We think the price is a good price, a fair price.
“Obviously our main concern was to make sure the building is properly looked after, properly renovated and treated with the respect and affection it deserves.”
The government revealed last November it had put the building on the market in a bid to cut costs for the taxpayer.
It has also vacated 36 other property holdings in London since May 2010, around 20 per cent of its office space in the capital – saving £90m.
Up to 100,000 visitors a year are expected to pass through the hotel, according to Spanish investor Rafael Serrano.
He said: “We anticipate the number of people will be between 40,000 and 50,000 guests a year and we hope it will attract another 50,000 visitors.”
The arch has been the focus of many national ceremonies over the last century, most recently the post-Olympic and Paralympic celebrations.
It was commissioned by King Edward VII as a tribute to his mother Queen Victoria and was completed in 1912.
Officials said they had “kept in touch with the palaces” over the plans but refused to say if the royal family had expressed a view.
Mr Maude said it was a great example of how government property could spur growth and would bring new jobs to London.
“Its astonishing appearance gives no clue to the somewhat less astonishing history when it has been serving for most of that time as slightly random office space for the government,” he said.
“It’s a really great shame that in the 100 years since it was opened there has been virtually no public access to the arch outside of government officials.
“When we came into office in May 2010 it was clear that without significant renovation, the arch was at risk of falling into disrepair.
“This would have been a tragic waste of a historic building.
“We were determined to find a real purpose to Admiralty Arch, one that would preserve it for future generations and would generate value for the taxpayer.”
He added: “Impressive monument that it is on the outside, for decades the arch has languished as a glorified, actually not that glorified, office space.
“A taxpayer-owned building that offered little value to the taxpayer.
“This arrangement will not only save money, it will bring this London landmark back to life, opening it up to the public and ensuring they have a say in its future.”
The restoration will use original drawings by architect Sir Aston Webb dating back to 1910.
PIC heritage expert Chris Miele said: “The transformation of the building into a destination and signature hotel will really increase appreciation of this well known but probably not much understood or appreciated London landmark.”