Why did Britain let minor diplomats live in a $22m apartment?

For once, the estate agent's marketing blurb does not exaggerate: "Resplendent apartment on Fifth Avenue. Glorious entertaining space. Splendid lobby. High ceilings. Fine architecture. Impeccable."

Unsurprisingly, this property, within a stone's throw of Central Park in the heart of Manhattan's most sought-after neighbourhood, carries an equally superlative price tag: a mere $22m or £15.7m.

Most would assume that at such prices, this palatial flat is the New York pied a terre of a billionaire oil magnate or the luxury hideaway of a media baron with a liking for Persian rugs and oil paintings.

The truth is altogether more arresting. The apartment at Number 4, East 66th Street is owned by Her Majesty's Government on behalf of the British taxpayer and serves as the residence of the consul general. Or at least it did until Jack Straw, the Foreign Secretary, called in the estate agents to put the property on the market with more than 80 of Britain's other diplomatic residences abroad.

Once the sale of the latest tranche of prime Foreign Office real estate, from Bombay to Bogota, is completed by the April deadline, it will have returned about £150m to the Treasury coffers.

Among the corners of foreign lands that will now no longer be British are: 13 residences in Paris; a three-bedroom house in Barbados and a surplus bit of the ambassadorial garden in Singapore. But the 7,000sq ft apartment on the Upper East Side, home of the New York aristocracy from Woody Allen to the city's new Mayor, Michael Bloomberg, is the jewel in the crown.

Among the attributes listed in the estate agent's descriptionare 14 rooms, 5 bedrooms, a 50ft banqueting room, a library, 60ft "grand gallery", an octagonal study and, inexplicably, 7.5 bathrooms.

High-society New York is said to be "agog" about who will eventually buy the opulent residence while Britons will be left wondering how "Our Man in Manhattan" ended up living in such style. As one New York real estate agent put it: "It's an incredible apartment, quite literally fit for a king. But how it became the home of a low-ranking diplomat is a joke."

Originally bought in the 1950s to house British ambassadors to the United Nations, the flat was abandoned during the 1980s by an ambassador who complained it was too far from the UN building.

Instead, it became the home of the consul general – a role considered somewhat lower down the diplomatic pecking order – in charge of consular emergencies and promoting Britain abroad.

All of which may be unfair on the current incumbent, Thomas Harris, who was knighted in the New Year honours after the "exceptional work" by him and his colleagues in the aftermath of the destruction of the twin towers on 11 September.

However, recognition of his efforts has not helped him to stay in the grace-and-favour apartment, where a string of receptions has been held in honour of visiting dignitaries including Dame Judi Dench.

The Foreign Office said Sir Thomas, who could not be contacted yesterday, had been moved to "temporary accommodation" in a cheaper flat to allow potential purchasers to look round. Diplomats added that the sale would lead to substantial savings for the Government.

"This exercise is about making the best use of the Foreign Office's budget," said a spokesman. "We want to get the best value for taxpayers."

Stribling & Associates, the Manhattan estate agent employed by the Foreign Office to find a buyer, declined to say whether any offers had been received after being sworn to secrecy by Whitehall.

Barbara Evans-Butler, the agent handling the sale, said: "I cannot comment. We have signed a confidentiality agreement with your government so we can't say anything."

Whoever does end up getting the keys to the flat, built in 1920 over an entire floor of the apartment block, will live in some style. It is furnished throughout with chandeliers, antique furniture, oil paintings and at least one grandfather clock.

A floor plan reveals a separate wine cellar, a powder room and two "maids rooms" which, in diplomatic language the current owners would be proud of, are part of a "gracious layout to separate public, private staff areas".

In keeping with its status as a home for only the wealthiest, the annual maintenance charge is $10,934 (£7,800).

Estate agents in New York are not the only ones who will be busy on behalf of HMG.

Residences throughout Europe, Asia, Africa and America have been earmarked for disposal, reflecting a general slimming of the Foreign Office presence around the globe.

In Muscat, Oman, two two-bedroom houses are expected to bring in £240,000 for the Treasury while in Jakarta, Indonesia, two staff flats worth £100,000 have been scheduled for sale.

The three-bedroom house in Bridgetown Barbados, reserved for diplomats at the High Commission, is on the market for £200,000.

Colonial residences in Africa, including two in Lagos, Nigeria's commercial capital, one in Lusaka, Zambia, and two in Capetown, South Africa, are to go. In Mbabane, the capital of Swaziland, the consular office has gone on the market after being found by London to be surplus to requirements and, in Dar es Salaam, an official residence is up for sale.

In Berlin, one residential property will be sold off. In Kuala Lumpur, a surplus piece of garden is up for grabs while in Valetta, Malta, an elegant four-bedroom diplomatic house worth £300,000 comes with a neighbouring plot of land.

Profits from this latest asset disposal will be spent on hi-tech communications including new computers in British postings.

The scale of the sell-off means many diplomats will no longer have the luxury of an official residence to put up guests or entertain and will have to compete with locals for more modest accommodation. An outcry is likely among traditionalists who believe the sale of elegant historic buildings amounts to a "dumbing down" of Britain's image abroad.

The Tories urged the Government not to sell too many historic buildings and to be "cautious in its approach".

Richard Spring, a foreign affairs spokesman, said: "I hope this is being done cautiously and carefully. We have made the mistake of selling off buildings in the name of modernisation before, only to regret that decision later."

Mr Straw believes that many colonial mansions are too opulent for today's needs, require large staffs and are costing too much to maintain.

The former National Union of Students' president is keen to modernise the image of the diplomatic service and recruit from a variety of backgrounds and ethnic groups. Even cities where a big diplomatic presence is maintained – including Washington, Ottawa and The Hague, homes are to be sold. In Washington, two diplomatic flats are for sale at $125,000 (£90,000) each, while in Tel Aviv, Israel, two properties are on the disposal list.

Since Labour came to power in 1997, more than 100 Foreign Office properties, including Glencairn, the British ambassador's residence in Dublin, have been sold. The 34-acre Glencairn estate, home to the ambassador since 1957, was valued at £30m when its sale capitalised on the country's property boom of 1998, amid pressure from the Treasury to trim budgets.

But in New York, at least, few could accuse Labour of encouraging bad local habits with its entry into the property market. The Fifth Avenue apartment, in the heart of gas guzzling America, lacks just one mod-con – a garage.