© REXThe President of Azerbaijan, Ilham Aliyev, and his wife Mehriban, on a visit to London in 2009
The Duke of York made private visits to the President of Azerbaijan, whose country is one of the most corrupt in the world, after forging links with him in his role as trade envoy.

The disclosures will add to questions over the Duke's relationships with the leaders of dubious regimes. He visited the Azerbaijan president eight times in five years, with two of the visits described as "entirely private".

The Duke's repeated visits to the state - ranked as one of the most corrupt in the world - were in the face of allegations of the torture of political opponents and rigged elections by the regime of President Ilham Aliyev.

Such has been the regularity of the Duke's visits that local media in Azerbaijan have speculated that he has business links to the oil-rich state, including a golf resort on the Caspian Sea. However, Buckingham Palace has denied this.

As recently as Monday of this week, Amnesty International demanded an end to the torture of activists demanding reforms in Azerbaijan similar to those seen in Tunisia and other parts of the Middle East.

The Duke is referred to on his visits as "the dear guest" and, in June 2009, he chartered a private jet and flew to the country for three days at an estimated cost to taxpayers of ยฃ60,000.

He is also reported to have visited a luxury spa owned by President Aliyev, which employs a blind Russian masseur described as the best in the world.

Azerbaijan also has links with the leader of Iran, Mahmoud Ahmadinejad.

The Duke's relations with the rich and powerful of the former Soviet states have come under intense scrutiny in recent weeks.

On Tuesday, it was disclosed that Kairat Kelimbetov, the head of Kazakhstan's ยฃ22.6billion ($36.6billion) sovereign wealth fund, met the Duke last April, then claimed that he had agreed to help Kazakhstan counter "stereotypes" that it was corrupt and a risky place to do business.

The Duke's sale of his former home, Sunninghill, to a Kazakh billionaire for ยฃ3 million above the asking price in 2007 also "raised eyebrows" in the royal palaces but the Duke "refuses to listen" to advice, it is claimed.

He has also been criticised for dealing with Gurbanguly Berdimuhamedov, the President of Turkmenistan, as the Duke's visits might have given credibility to a regime ranked the sixth most corrupt in the world. By comparison, Azerbaijan ranks 44th out of 178.

The Duke has reportedly told Goga Ashkenazi, a Kazakhstan-born friend, he was "very worried" about his ability to continue in the post.

However, it is his relationship with the convicted paedophile and disgraced financier Jeffrey Epstein which has generated most controversy, ever since a photograph of him with his arm around Epstein's 17-year-old "personal masseuse", who claimed she had been groomed for underage sex by the billionaire, was published more than a week ago.

A spokesman for Buckingham Palace said: "The Duke's work in Azerbaijan focuses on oil, gas and energy security issues, all of which have great potential to deliver substantial opportunities for British companies.

"His work there is highly valued and he continues to play a role, at the request of Government, in helping to develop trade relations between our two countries."