Bahrain’s King Hamad al-Khalifa (pictured) and Swaziland's King Mswati III are both expected to attend today’s event. The former is accused of human rights violations in Bahrain following a crackdown on political protests, while King Mswati is the world’s 15th richest monarch (with a personal fortune of around $100m), while 1.2 million of his subjects live in abject poverty.
King Mswati is also Africa’s last absolute monarch, and pro-democracy campaigners have been fighting for political parties and elections in the country.
Buckingham Palace refused to comment on today’s lunch, but the Foreign Office have released a statement.
In it, they say: "On human rights we support the reforms already under way in Bahrain and we want to help promote that reform.
"We have consistently encouraged the Bahraini government to take further urgent steps to implement in full the recommendations of the Independent Commission of Inquiry as his majesty the King has committed to doing.”
However, campaigner Peter Tatchell has criticised today’s guest list saying, "Inviting blood-stained despots brings shame to our monarchy and tarnishes the Diamond Jubilee celebrations.
"It is a kick in the teeth to pro-democracy campaigners and political prisoners in these totalitarian royal regimes."
Many of today’s lunch guests will then be invited to an evening banquet, hosted by Prince Charles and the Duchess of Cornwall.
Earlier this week, Spain’s Sophia revealed that, despite her invitation, she will not be attending today’s ceremonies because of a dispute over fishing rights off the coast of Gibraltar.