At Westminster Hall in London, on the very spot where England's last absolute monarch was convicted of torture and tyranny, the world's most absolute dictator presumes to lecture our present leaders on the sins of the democratic society that has evolved in the centuries since the overthrow of Charles I. We are paying for this privilege, because the monarch of the Holy See is here on a state visit from 16-19 September. But the Holy See is a "Santa Claus" state - no matter how many believe in it, it does not exist.

The Vatican, as any tourist can tell, is not a state at all: it is a palace, surrounded by gardens, about the size of a large golf course. In law (the 1933 Montevideo Convention), a state must have a people - and there are no Vaticanians. In this Roman enclave of celibates, no citizen is born other than by accident. It has no "territory" - another statehood requirement - other than the 108 acres conveyed inviolably to it by Mussolini in 1929 as part of a sordid deal with the pro-fascist Pius XI to destroy democracy in Italy. This is described as the "Lateran Treaty" although it is not, as a matter of law, a treaty (an agreement between sovereign states) at all. It is a deal between Italy and its Church, and obviously has no legal effect on the UK, which has never been a party to it. Nonetheless, it is on this dubious document that the Vatican today pins its claim to statehood. Its most recent sovereignty statement to the United Nations reads:

"The Holy See exercises its sovereignty over the territory of the Vatican City State, established in 1929 to ensure the Holy See's absolute and evident independence and sovereignty for the accomplishment of its worldwide mission, including all actions relating to international relations, cf: Lateran treaty, preamble and articles 2-3."

Separate powers

So when Henry Bellingham MP, a junior minister at the Foreign and Commonwealth Office (FCO), stated in a letter to the New Statesman last week: "It is not the case that Britain recognises the Vatican because of the Lateran Treaty, nor could it be," he spoke with forked tongue. The UK resumed diplomatic relations in 1914 with the Holy See as an international entity, but not as a state. It then had no territory because the Risorgimento had extinguished the papal states in 1870, and even the Italian courts have recognised that the Vatican could make no claim again to statehood until its deal with Mussolini in 1929, because until then it possessed not a square inch of land.

So Bellingham is playing with words: the Lateran "treaty" is crucial to recognition of the Holy See as a state, and to the government's invitation to the Pope as a head of state, for the simple reason that it is the only basis on which the Holy See claims to be a state. But the Foreign Office appears unaware, either of its history or of its terms. When I made a Freedom of Information (FoI) request for documents relating to the expensive decision to keep separate UK embassies for the Vatican and for Italy, a Foreign Office official wrote:

"the Lateran pact guaranteed the full sovereign independence of the Vatican City in international law . . . under the terms of this treaty, it is not possible for ambassadors to Italy to be representative simultaneously to the Holy See - hence the need to maintain two separate embassies in Rome . . . under the Lateran pact it is impossible for any state to merge its embassies to Italy and the Holy See . . . they are in separate buildings . . . in accordance with the Lateran Pacts, the two ambassadors' residences remain located in separate parts of Rome."

This is all nonsense - there is nothing at all in the Lateran Treaty that requires this separation. Importantly, Bellingham now admits that this confident assertion by the Foreign Office was "a mistake". Instead, he tells us that the FCO deferred to "the practice of the Holy See". Vatican "practice" has no meaning or effect in law, and by kowtowing to it, the FCO has caused the taxpayer to fund an entirely unnecessary embassy and ambassadorial residence in Rome.

Curious bluff

The matter was raised in 2004, after the UK relinquished its luxurious villa near the Appian Way which had served as its embassy to the Holy See. It proposed to save money on rent, security, gardeners and assorted flunkies by relocating it to our embassy in Italy. Cardinal Angelo Sodano, then secretary of state to Pope John Paul II, protested that this would be a breach of the Lateran Treaty. Incredibly, the UK capitulated. It is astonishing that the FCO should have been such a pushover on this matter, conceding a claim that was wrong in law and based on a treaty to which the UK was not a party.

Although the Foreign Office website claims that the embassy to the Vatican conducts a valuable "dialogue" on human rights, it refuses to divulge what is said. Another FoI request has been refused, on the grounds that disclosure "would be likely to prejudice effective relations between the UK and the Holy See". Decoded, this probably means that exposure would cause embarrassment to the FCO - perhaps by revealing that there has been no dialogue at all on such important issues as Vatican responsibility for the rape of thousands of children, or for promoting homophobia by denouncing gay people as "evil", or for objecting to condom use to prevent HIV/Aids in Latin America and Africa.

If there is to be such dialogue - and for any western government that takes human rights seriously, there certainly should be - there is no reason why it cannot go on within the concrete walls of the UK embassy to Italy. William Hague should call the Curia's bluff and merge the two UK embassies in Rome.

Geoffrey Robertson, QC is the author of “The Case of the Pope" (Penguin Special, £5.99)