The Queen was accused of making a catastrophic error of judgment today by dining with the King of Bahrain, whose regime is accused of a catalogue of human rights abuses.
The Middle East ruler is one of a number of foreign monarchs criticised for their human rights records or extravagant lifestyles who have been invited to dine with the British Royal Family.
Buckingham Palace's guest list for the lunch, being held at Windsor Castle, represents the biggest gathering of foreign royals in the UK since the Duke and Duchess of Cambridge's wedding last year.
Bahrain's King Hamad Al-Khalifa has been condemned as a despot by former Foreign Office minister Denis MacShane in the run up to the lunch.
He said many would regret Foreign Secretary William Hague's decision to approve the inclusion of the Middle East ruler.
But the Foreign Office has stressed it is supporting Bahrain in its attempts to improve its human rights.
On Thursday Peter Tatchell decried any invitation for the Bahraini royals as "outrageous", telling the Huffington Post UK he expected eight dictators to be on the guestlist.
"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."
Guests from controversial regimes include Swaziland's King Mswati III, Sheikh Nasser Mohamed Al-Jaber Al-Sabah of Kuwait and Prince Mohammed Bin Nawaf Bin Abdulaziz Al Saud of Saudi Arabia.
Mr MacShane said: "Arab nations must let their citizens vote in free elections and let them speak without fear of arrest, torture or death.
"For too long we have turned a blind eye to the repression carried out under the rule of royals in Arabia.
"The FCO should protect the British Queen rather than expose her to having to dine with a despot."
Members of the British monarchy attending the lunch include the Duke of Edinburgh, Duke and Duchess of Cambridge, Prince Harry, the Duke of York and Princesses Beatrice and Eugenie and the Earl and Countess of Wessex.
But the King of Bahrain will not be present at a Buckingham Palace dinner for the foreign royals being hosted by the Prince of Wales and Duchess of Cornwall on behalf of the Queen.
The confirmed members of the British monarchy attending the evening event are the Duke of York, Earl and Countess of Wessex, Duke and Duchess of Gloucester, Duke of Kent and Prince and Princess Michael of Kent.
The popular uprisings that toppled a succession of Arab dictators across the Middle East last year failed to ignite significant protests in the Arab Peninsula.
But in Bahrain there were major demonstrations with protesters calling for a greater say in government, these were violently put down by Saudi forces called in by the regime.
The decision to stage the Formula One Grand Prix in the country last month re-ignited tensions and there was further violence.
Bahrain has said it aims to improve its human rights after its officials held an inquiry into the handling of last year's protests and produced recommendations.
Swaziland's King Mswati III, is accused of having a lavish lifestyle while his people starve.
Protests were held outside the African ruler's exclusive London hotel earlier this week where he is said to be staying with an entourage of more than 30 people.
Recent reports by Amnesty International highlighted a wave of repression in Saudi Arabia as the authorities have cracked down on protesters and reformists.
While Human Rights Watch have criticised the Kuwaiti authorities for the suspension of a daily paper and the conviction of its editor for alleged incitement.
European Royals are well represented on the guest list, King Carl XVI Gustaf and Queen Silvia of Sweden, King Harald V and Queen Sonja of Norway, Prince Albert II of Monaco and his wife Princess Charlene have all been invited.
Also amongst the guests are Grand Duke Henri and Grand Duchess Maria Teresa of Luxembourg, Prince Hans-Adam II of Liechtenstein, Queen Beatrix of Holland and King Albert II and Queen Paola of Belgium.
But Queen Sophia of Spain is missing as she was ordered by her government to turn down the invitation.
The last minute snub was in response to a reported trip the Earl of Wessex will make to Gibraltar, a UK overseas territory which Spain wants returned to its sovereignty.
Royals from across the globe also feature from Emperor Akihito and Empress Michiko of Japan to Thailand's Crown Prince Maha Vajiralongkorn and his wife Princess Srirasm.
A Foreign Office spokesman said Britain's close relationship with Bahrain "... allows us to have a full and frank discussion on a range of issues including those where we have concerns.
"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 the his majesty the King has committed to doing.
"This includes bringing to account those individuals responsible for human rights abuses."
Here is the full list of British and foreign royals attending the dinner for sovereign monarchs.
British Royal Family
HRH The Prince of Wales
HRH The Duchess of Cornwall
HRH The Duke of York
HRH The Earl of Wessex
HRH The Countess of Wessex
HRH The Duke of Gloucester
HRH The Duchess of Gloucester
HRH The Duke of Kent
HRH Prince Michael of Kent
HRH Princess Michael of Kent
HRH Princess Alexandra, The Honourable Lady Ogilvy
HM The Sultan and Yang Di-Pertuan of Brunei
HM Raja Isteri Pengiran Anak Hajah Saleha (Brunei)
HM King Simeon II of the Bulgarians
HM Queen Margarita of the Bulgarians
HM Queen Margrethe II of Denmark
HRH Prince Henrik, The Prince Consort (Denmark)
HM King Constantine of the Hellenes
HM Queen Anne-Marie of the Hellenes
HM The Emperor of Japan
HM The Empress of Japan
HM The King of the Hashemite Kingdom of Jordan
HM Queen of the Hashemite Kingdom of Jordan
HH Sheikh Nasser Mohamed Al-Jaber Al-Sabah of Kuwait
HM King Letsie III of Lesotho
HM Queen Masenate Mohato Seeiso of Lesotho
HSH Prince Hans-Adam II of Liechtenstein
HRH The Grand Duke of Luxembourg
HRH The Grand Duchess of Luxembourg
HSH The Prince of Monaco
HSH The Princess of Monaco
HRH Princess Lalla Meryem of Morocco
HM The King of Norway
HM The Queen of Norway
HM King Michael I of Romania
HRH Crown Princess Margarita of Romania
HRH Prince Mohamed Bin Nawaf Bin Abdulaziz (Saudi)
HM King Mswati III of Swaziland
HRH Inkhosikati LaMbikiza of Swaziland
HM The King of Sweden
HM The Queen of Sweden
HRH The Crown Prince of Thailand
HRH Princess Srirasm of Thailand
HM The King of Tonga
HM The Queen of Tonga
HH The Crown Prince of Abu Dhabi
HRH The Crown Prince of Yugoslavia
HRH The Crown Princess of Yugoslavia