Prince Andrew faces international censure after flying out yesterday on a secret visit to meet the controversial president of Azerbaijan.

The Queen's son flew out of the UK on a private jet for talks with billionaire despot Ilham Aliyev, who has been repeatedly accused of appalling human rights abuses.

It is understood that the royal will stay in the capital, Baku, until Sunday and his 'private' four-day trip includes at least one face to face meeting with the leader. When visiting Azerbaijan Andrew is known as 'the dear guest'.

Close ties: Prince Andrew and Azerbaijan president Ilham Aliyev during one of their meetings in 2009

His visit was not publicised in the list of official royal engagements in advance and last night Buckingham Palace would only say: 'By long standing convention we do not confirm or comment on private travel by members of the Royal Family.'

However it is understood that taxpayers are not being forced to foot the bill for the jolly, aside from the cost of security.

Details of the trip only emerged after a British Government source tipped off the pressure group, Platform, which campaigns against social and environmental abuses associated with the energy industry.

Its spokesman, Emma Hughes, accused the prince of having a 'cosy relationship' with President Aliyev and demanded to know in what capacity he was visiting Azerbaijan.

Andrew was forced to give up his globe-trotting royal role as a UK trade envoy in 2011 after years of public criticism.

While his efforts were lauded by some respected names in the business community, he was also repeatedly accused of wasting taxpayers' money on chartering costly private jets and helicopters - including £387,000 in his last few months in the job.

Some of his business trips were also noted to coincide with golfing trips or private holidays.

The prince also faced scrutiny over claims he was 'cashing in' on connections he had developed through his role including the sale of his Berkshire home for £15 million - £3million over the asking price - to the son-in-law of the controversial Kazakhstan president, a personal friend and goose hunting partner.

The final nail in the coffin was the furore over his close friendship with Jeffrey Epstein, a billionaire US financier who was convicted and jailed for soliciting prostitution from underage girls. The pair were photographed together in New York after Epstein had been released from prison.

During his decade as the UK's Special Representative for Trade and Industry he also forged a close relationship with the President of Azerbaijan, an oil and gas-rich former Soviet state.

The Duke of York speaking at World Economic Forum in Baku, Azerbaijan, at the dinner hosted by Mr Aliyev

Officially, he has now met with him on 12 occasions, although it is believed that he has also enjoyed numerous private encounters too.

In June 2009 Andrew spent an estimated £60,000 of public money on chartering a luxury private jet for a three-day visit.

And in November 2012 the Mail revealed how the prince had even made a covert stop-off to visit the president en route to an official tour of the Middle East.

On another earlier stay he was reported to have visited a luxury spa owned by President Aliyev, which employs a blind Russian masseur described as having the best hands in the world.

And in 2013 this newspaper also revealed that Andrew had been given a valuable ornamental sword and a box of caviar by Aliyev when was guest of honour at his dinner table.

The Prince is also friendly with the president's wife Mehriban, and her two glamorous daughters, one of whom, Leyla, is married to the son of a Russian oligarch and lives in a penthouse overlooking Hyde Park in London.

The disclosures have added to the disquiet over the prince's relationships with the leaders of dubious regimes, as Azerbaijan is considered to be one of the most corrupt countries in the world.

The regularity of his visits have also led media in the former Soviet state to speculate that the Queen's son may have business links to the oil-rich state, including a golf resort on the Caspian Sea. Buckingham Palace has vehemently denied this.

News of his latest trip has attracted condemnation from pressure groups concerned by Azerbaijan's appalling human rights record.

Aliyev, who inherited the presidency from his father, has been accused of torturing his political opponents, rigging elections and curtailing media freedom.

Last October presidential elections were held in the country which saw 143 political campaigners jailed. Videos also emerged of ballot boxes allegedly being stuffed by regime supporters.

Prince Andrew is not the only high profile British figure who has close links with the Aliyev regime. This August it was announced that Tony Blair is being paid to advise the Azerbaijani government and several oil companies - including BP - on the PR challenges they face in building the Euro-Caspian Mega Pipeline, a huge gas infrastructure that will run from Azerbaijan to Italy.

Emma Hughes, Energy Campaigner at campaign group Platform said: 'It's shameful that both Prince Andrew and Tony Blair are so chummy with the Azerbaijani autocrat.