President Mitterrand of France warned Margaret Thatcher privately that a reunited Germany might “make even more ground than Hitler had” only a few weeks after the fall of the Berlin Wall, newly declassified documents reveal.

In papers due to be published by the Foreign and Commonwealth Office tomorrow, after a year of deliberation by Whitehall officials, the scale of Anglo-French fears on German reunification is laid bare.

At a lunch at the Élysée Palace on January 20, 1990, Charles, now Lord, Powell, the then foreign affairs adviser to Mrs Thatcher reports in a memo that Mr Mitterrand talked about how reunification would cause the re-emergence of the “bad” Germans who dominated Europe.

According to the memo, Mr Mitterrand said at one point that if Helmut Kohl, the Chancellor of West Germany at the time, were to get his way, a unified Germany could win more ground than Hitler ever did and that Europe would have to bear the consequences.

Mr Mitterrand warned Mrs Thatcher that if Germany were to expand territorially, Europe would be back to where it had been one year before the First World War.

The Berlin Wall fell in November 1989 and Germany was not formally reunited until October 1990. The private meetings between the then Prime Minister and Mr Mitterrand followed Mr Kohl’s ten-point plan for reunification.

Mrs Thatcher’s opposition to reunification, and her disagreement with the Foreign and Commonwealth Office over the issue, is also revealed in the 500 papers. One document refers to her expressing horror on hearing incorrect reports that the members of the Bundestag in Bonn sang Deutschland über alles to celebrate the fall of the Wall.

In another document she is reported as finding the views of Sir Christopher Mallaby, the British Ambassador to Bonn, “alarming”, expressing astonishment that he appeared to welcome the prospect of a united Germany.

The documents show that diplomats from the Foreign Commonwealth Office realised as early as January 1989 that German reunification was a possibility. After the Wall fell they feared that Mrs Thatcher was adopting a stance so shrill that no one was listening to her.

The decision to make the papers public now (Britain normally issues secret official documents only after 30 years) is being viewed as an attempt to show that British diplomats were positive about reunification in the early stages.

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