If you're reading this on a packed, stalled train, late for work, eating a stale station bacon roll, imagine what life could have been like. If France and Britain had gone ahead with an audacious plan in the 1950s to merge the two countries, the train might have been on time, and faster, the croissants better, but then again, with Paris's current unemployment problem, there might not have been a job to go to.

Newly uncovered documents have shocked historians by revealing that in the 1950s, Britain and France discussed the possibility of uniting and Queen Elizabeth II becoming France's head of state.

In September 1956, the French prime minister Guy Mollet, a former English teacher and wartime resistance fighter, came to London to discuss the possibility of a union with his British counterpart, Anthony Eden. According to an investigation by BBC Radio 4's Document programme, Eden turned down the idea but gave positive consideration to Mollet's next suggestion - that France should be allowed to join the Commonwealth.

A government document dated September 28 1956 shows Eden recommended "immediate consideration" of France's Commonwealth bid and Mollet "had not thought there need be difficulty over France accepting the headship of Her Majesty [Queen Elizabeth II]; [and] that the French would welcome a common citizenship arrangement on the Irish basis".

At the time of Mollet's proposals, France was facing economic difficulties, an escalating Suez crisis and a bloody Algerian war. Gamal Abdel Nasser's nationalisation of the Suez canal was perceived as an act of war by Mollet, who was also infuriated by the Egyptian president's support of Algeria's National Liberation Front. The French prime minister was seeking to line up his international allies, turning to Britain, a staunch French ally during two world wars.

The discussions between Mollet and Eden came to nothing, and a year later France was one of the founding members of the Common Market, the forerunner of the European Union. Britain was not among the original members.

Winston Churchill's 1940 offer of a Franco-British union is well known. But French academics and politicians were yesterday shocked to hear of Mollet's bid - contained in documents which were declassified 20 years ago but had lain unnoticed in the National Archives in London.

Henri Soutou, professor of contemporary history at Paris's Sorbonne University said: "Really I am stuttering because this idea is so preposterous. If this had been suggested more recently Mollet might have found himself in court."

Nationalist MP Jacques Myard said: "I had a good opinion of Mr Mollet before. I think I am going to revise that opinion."

Gilles Savary, socialist party MEP and EU adviser to the presidential candidate Ségolène Royal, said the merger would be unthinkable today. "French and British history shows that a merger of the countries would today be politically and diplomatically out of the question."

But Jean-Pierre Maulny, deputy head of Paris's Institute for International and Strategic Relations, said the proposal seemed "very logical". He said if France and Britain moved on from their differences over Iraq, globalisation and liberalism, "this type of proposal could even come to the surface again". The former Europe minister Denis MacShane said the revelation showed the "best bits of history are its footnotes". He said: "France and England are like an old married couple who often think of killing each other, but would never dream of divorcing."