David Cameron and the Prince of Wales flew to Saudi Arabia yesterday alongside world leaders eager to pay their respects after the death of King Abdullah, despite uproar over the UK’s tacit declaration of a state of “national mourning” for a man regarded by many as a tyrant.Union flags were flown at half-mast over Buckingham Palace, the Houses of Parliament and Downing Street on Friday, despite the Saudi monarch’s reign over a country in which there is widespread discrimination against women, a lack of free speech and persecution of religious minorities and dissidents, coupled with a brutal criminal justice system.

Graham Bartram, chief vexillologist (flag expert) at the Flag Institute, said the UK’s public display of mourning could have been avoided without causing offence. “Maybe nobody in government knew that Saudi Arabia doesn’t half-mast its flag,” he said.

The country’s importance as a ally of the West, and its key role in determining global oil prices as the world’s biggest exporter helped ensure fulsome tributes.

King Abdullah dead: Reaction from around the world

Mr Cameron met the new King Salman and other members of the royal family in Riyadh yesterday. US President Barack Obama, French President François Hollande, Crown Prince Naruhito of Japan, King Felipe VI of Spain, King Abdullah of Jordan, Crown Prince Frederik of Denmark and King Willem-Alexander of the Netherlands are among others to have paid their condolences or who are on their way to do so.

The new monarch, 79, has said he plans to continue in a similar vein to his predecessor.

Joe Stork, deputy Middle East director of Human Rights Watch, said: “King Salman should move the country forward by ending intolerance for free expression and rooting out gender and sectarian discrimination.”

Conservative MP Sarah Wollaston, a member of the all-party group on human rights, said: “The flying of the Union flag at half-mast is of very large importance.

“It reflects a kind of national mourning. I just don’t think  the Saudi human rights record  merits that.”