The Queen's Diamond Jubilee event has triggered protests as it is expected to include some controversial monarchs.
Guests are expected to include Swaziland's King Mswati III, who is accused of leading a lavish lifestyle while his people go hungry.
Another controversial figure expected to attend is Bahrain's King Hamad Al-Khalifa, whose country is in a state of civil unrest.
Yesterday, a group of Swazis living in the UK protested outside London's luxurious Savoy Hotel, where King Mswati is said to be staying.
Twice baked souffle, line caught sea bass and Duchy of Cornwall veg on the menu for monarchs at sovereign dinner at Buckingham Palace
The Queen is holding a lunch for monarchs from around the world celebrating her Diamond Jubilee, but some of her guests are raising eyebrows
Queen Sophia of Spain will not be attending Friday's Diamond Jubilee lunch after being ordered by her government to reject the invite.