Traumatised by Suez and the fighting in Algeria, a desperate French Prime Minister floated the idea of merging with Britain in 1956 and installing the Queen as head of state of the two countries, the BBC will report tonight.

Records of conversations between Anthony Eden, the British Prime Minister, and his Cabinet Secretary, Sir Norman Brook, show that the idea was swiftly dismissed but that serious thought was given to a secondary proposal to make France a member of the Commonwealth.

The minutes have been available to historians for 20 years in the National Archives but their contents was not widely known, the BBC reported today. The discovery has surprised historians in France, where no evidence of the proposal, made by Guy Mollet, the Prime Minister, exists.

The Cabinet record of Mr Mollet's visit to Britain on September 10, 1956, reads as follows: "When the French Prime Minister, Monsieur Mollet was recently in London he raised with the Prime Minister the possibility of a union between the United Kingdom and France," the BBC reported.

A subsequent note, from September 28, 1956, describes a conversation between Mr Eden, a well known Francophile, and Sir Norman Brook:

"Sir Norman Brook asked to see me this morning and told me he had come up from the country consequent on a telephone conversation from the Prime Minister who is in Wiltshire. The PM told him on the telephone that he thought in the light of his talks with the French:

"That we should give immediate consideration to France joining the Commonwealth.

"That Monsieur Mollet had not thought there need be difficulty over France accepting the headship of her Majesty.

"That the French would welcome a common citizenship arrangement on the Irish basis."

The offer of an Anglo-French merger — "an indissoluble union" — was made by Winston Churchill in the spring of 1940, as Nazi Germany threatened to conquer both countries, and historians and politicians said today that the Mollet idea was another curio in a long and intense relationship. It prefigured the formation of the European Economic Community, the forerunner of the EU, by just a year.

"I liken the French/British relationship to a very old married couple who often think of killing each other but would never dream of divorce," said Denis MacShane, the former Europe Minister, today. "This is an example of the tortured romance between our two countries that has been going on since William the Conqueror colonised Britain 1,000 years ago."

Mr MacShane also suggested that for all the hostile posturing in the press of both countries, the royal family would have had a loyal following in France — where the film The Queen has been a hit — and that the populations of each country have a strong mutual respect.

Kevin Ruane, a professor of modern history at Canterbury Christ Church University who has studied Anglo-French postwar relations, said Mr Mollet's suggestion had been known to historians of the subject for some time and illustrated the intense strain of the looming Suez crisis and the agitations of Gamal Abdel Nasser, the Egyptian President, who was funding the Algerian uprising against French colonial rule.

"For the British audience I think this shows that France was extremely worked up over the Suez thing. It wasn't just Anthony Eden," he said. "This shows desperate men at a desperate moment, coming up with a knee-jerk reaction."

"I think if you were to sit down and work out the practicalities of such a relationship you would see it as a marriage made in haste and repented at leisure. You simply cannot put two such nationalist entities, as they then were, together and expect them to get along."

"A Marriage Cordial" will be broadcast on BBC Radio 4's Document at 8pm tonight, Monday, January 15.

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