Prince Andrew and the Arab prince with a stake in Queen’s £3 windfarm 

The Duke of York’s controversial job as Britain’s international trade ambassador was hanging by a thread last night as more damaging revelations emerged about his conduct.

New evidence of a clear conflict of interest between his role as ambassador and his own business affairs have been obtained by the Sunday Express.

He is already beset by concerns about his close friendship with the Abu Dhabi royals and we have learned of a “business trip” undertaken on behalf of British industry yet funded by the Saudi Royal family.

Prince Andrew, trade representative for the government body UK Trade and Investment, was an expenses-paid guest of the Saudis last year.

The trip was public knowledge and listed as a UKTI trip but the UKTI did not pay for it, as would be normal practice, opening the Duke to claims that his paying hosts may expect special treatment in return.

The revelations come amid embarrassing disclosures in the WikiLeaks scandal. Claims in the cables by a US diplomat that his behaviour “verged on rude” as he rubbished an anti-corruption probe into a Saudi arms deal have caused acute embarrassment to Buckingham Palace.

Yesterday the Duke was mired in yet more controversy as Britain’s former deputy head of mission in Bahrain, Simon Wilson, said the style in which he carried out his trade role “beggared belief” and he used it to “plough his own furrow”.

Mr Wilson’s claims confirmed our own findings of a potential conflict of interest.

Buckingham Palace last night confirmed that the Saudis laid on five star accommodation for the Duke during his short trip.

UKTI paid just £400 “communication cost” towards the trip. The Duke’s many business trips for UKTI have won him the nickname “Air Miles Andy”. Its annual accounts show a number of trips last year, notably to Singapore in September (costing £31,100), to New York in June (£11,700), to Azerbaijan in June (£7,600) and to Algeria in May (£4,700).

The “free trip” to Saudi in September stands out on the UKTI balance sheet.

Graham Smith from the anti-monarchist group Republic said the Saudi trip “raises serious questions about why the Saudi trip was financed in a different way to all the other trips. Why would the Saudis pay? One presumes because they want something in return at some point”.

Buckingham Palace has strongly rebutted any suggestion of wrongdoing or a conflict of interest by the Duke.

A spokesman said: “We cannot be more robust in our response to an allegation that the use of Saudi government hospitality represents a conflict of interest when it absolutely does not.”

It has emerged that an Arab royal who frequently entertains the Prince has secured a multimillion-pound stake in the world’s biggest wind farm in a deal that could earn a fortune for the Royal Family as the Crown Estates are paid rental for the undersea cables taking power from the wind farms to the mainland.

Crown Prince Sheikh Mohammed bin Zayed Al Nahyan, the brother of Abu Dhabi’s ruler, who has been friends with Andrew since their days at Gordonstoun School in Scotland, owns 20 per cent of the planned £3billion London Array wind farm in the Thames Estuary.

Prince Andrew is also facing claims in the High Court that a Kazakh billionaire Timur Kulibayev used laundered money for the £15million purchase of his former home “Southyork” at Sunninghill Park near Windsor.

Kulibayev paid £3million more than the asking price, only to let it fall into decay. As trade ambassador the Prince has visited Kazakhstan on several occasions.