Behind a 19th-century facade in Regent Street, London, lies a gleaming office complex that controls the Crown Estate. Its mission: to raise £250m a year for the public from the land and property of the monarch by 2012.

However, executives there have given princes Andrew and Edward remarkably good deals on their mansions, both a few miles from Windsor Castle.

The Sunday Times has unearthed details of a series of “sweetheart” deals that have potentially saved millions of pounds for members of the royal family.

Graham Smith, campaign manager for Republic, which wants an elected head of state, said: “It’s quite clear the Crown Estate is giving the royals preferential treatment, which is totally inappropriate.

“This land and property has never been the personal property of the Crown. It’s there to raise revenue for the country.”

The Sunday Times has established that Beatrice and Eugenie, the daughters of Prince Andrew, stand to inherit the lease to a rent-free Crown Estate royal residence in Windsor Great Park.

Princess Beatrice already has the use of a rent-free state-owned apartment at St James’s Palace while she is a student. The apartment has been refurbished for £250,000.

The Crown Estate, which dates from 1066, says it has sought independent valuation for its private deals with the royal family, but admits that the specific circumstances of some properties can mean reduced rates for royalty.

Perhaps the deal most at odds with its remit to protect both the natural heritage and the taxpayer’s interests involves Sunninghill Park, the former marital home of the Duke and Duchess of York. Thanks to the Crown Estate deal, Prince Andrew walked away with a £15m windfall - and the mansion near Ascot is now abandoned and in decay.

The Crown Estate initially sold a 125-year lease on a parcel of green belt land for Sunninghill Park to the Queen for an undisclosed fee. The palace overrode local opposition to secure planning permission for the a red-brick ranch-like mansion.

When Prince Andrew wanted to sell some years later he realised there was a snag: the Crown Estate owned the freehold. Trustees acting for Prince Andrew suggested the Crown Estate might like to sell it. The agreed price in August 2003 was a mere £12,265.

The Crown Estate defended the deal last week, saying there was “no reason” to keep the freehold and the price was independently assessed. The mansion languished on the market for four years and was then bought in September 2007 for £15m - £3m more than the asking price.

Inquiries by The Sunday Times established that the most likely buyer was Timur Kulibayev, the billionaire son-in-law of the Kazakh president, Nursultan Nazarbayev.

The sale was a welcome windfall for Prince Andrew because by then he had snapped up another Crown Estate deal – a 75-year lease for the Royal Lodge, the Queen Mother’s former residence. The pink-washed lodge has 30 rooms, staff quarters and grounds of 100 acres.

The cost of the lease was just £1m, but Prince Andrew embarked on a £7.5m refurbish-ment programme. Under the terms of the lease, it can be passed to his daughters or to his widow.

Crown Estate officials stated they were unable to secure the “highest market value” for the property because of security problems. The royal chapel – where services are held for the royal family – is in the grounds of the lodge, which meant the property could not be offered on the open market.

Prince Andrew’s mansion is, however, relatively modest compared with the Crown Estate property secured by his brother Edward in yet another bargain deal. In March 1998 he was given a 50-year lease on Bagshot Park in Surrey, a 50-room former royal residence. The Crown Estate said it did some “selective marketing” beforehand, and the £90,000-a-year deal was independently assessed.

However, Edward went on to charge a pharmaceutical company £80,000 a year for the rent of the estate’s stable block. It meant he was in effect paying rent of a net £192 a week on the property. He has now extended the lease to 150 years for £5m, with a peppercorn rent. Property agents say such properties would typically sell for about £30m.

Crown Estate officials admit that their decisions are not driven entirely by maximising revenue, saying they also place value on having royals in residence.

Sunninghill Park stands as a cautionary tale. Since it was sold, the property has not been occupied. Padlocks have been placed on the gates after thieves stole paving stones and stripped its columns down to the metal.

Bracknell Forest council said it was investigating the property and whether any action might be required under the Housing Act, whereby properties can be seized if they are unsafe or causing significant problems. A neighbour said last week: “The building just appears to have been left to rot.”

The Crown Estate said: “We don’t feel the royal family have got preferential deals, but sometimes we can’t let properties on the open market. We have done the best deals that we can. We seek independent valuation and act on that advice.”

Queen ejected room snatchers

The Queen once raced down the corridors of Windsor Castle dressed only in a bathrobe to turf a couple of minor royals out of a bedroom suite permanently reserved for her mother.

The monarch had “a face like thunder” as she ordered the unfortunate pair’s luggage to be removed immediately.

The tale is told by Father Michael Seed, the Catholic priest who for more than 20 years acted as an unofficial chaplain to MPs, members of the royal family and celebrities, in an exclusive extract from his new autobiography, Saints and Sinners.

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