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 head of state and her family sat down to lunch with the Middle East ruler and other controversial foreign royals as they celebrated her Diamond Jubilee.

The event was supposed to be a rare meeting of monarchs to celebrate the 60-year milestone, but it has been overshadowed by strong criticism from campaigners about those invited to the Windsor Castle event.

Guests from controversial regimes include Swaziland’s King Mswati III, the former prime minister of Kuwait Sheikh Nasser Mohammad Al-Sabah, who stepped down over a corruption row, and Prince Mohammed Bin Nawaf Bin Abdulaziz Al Saud, Saudi Arabia’s Ambassador to Britain.

The anti-monarchy group Republic, along with human rights groups, has accused Bahrain’s government, dominated by members of its royal family, of orchestrating the violent suppression of pro-democracy protesters last year.

When the country’s King Hamad Al-Khalifa arrived at Windsor Castle he was personally greeted by the Queen, who smiled as she shook his hand and the pair laughed as they shared a joke.

Republic’s chief executive Graham Smith said: “The Queen cannot hide behind protocol and precedent, this is a crisis of her own making.”

The popular uprisings that toppled a succession of 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 a 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 record after its officials held an inquiry into the handling of last year’s protests and produced recommendations.

King Mswati 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. 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.

Human Rights Watch have criticised the Kuwaiti authorities for the suspension of a daily paper and the conviction of its editor for alleged incitement.

Denis MacShane, a former Foreign Office minister, was another vocal critic of the guest list, which included the King of Bahrain, and laid the blame at the door of the Foreign Office.

He said: “Given the amount of blood on the hands of the royal regime in Bahrain it’s a shame he will stain the white linen of Windsor Castle at this event.

“It’s the responsibility of the Foreign Office to decide who comes, it’s nothing to do with Her Majesty.”

The Queen and Duke of Edinburgh greeted their guests personally when they arrived, patiently waiting outside the Castle’s Waterloo chamber where the pre-lunch reception was held.

First to arrive was Prince Hans-Adam II of Liechtenstein, soon followed by Grand Duke Henri and Grand Duchess Maria Teresa of Luxembourg.

The Grand Duke and Duchess were warmly greeted by the Queen and Duke with handshakes and double kisses - a display of affection that set the tone for many of the welcomes.

King Harald V of Norway kissed the Queen’s hand when he and his wife Queen Sonja met the monarch and she replied with a beaming smile.

PA