PARIS - Twenty years after the fall of the Berlin Wall, newly released diplomatic files reveal the extent to which Germany's supposed friends in London and Paris were fearful of the country's reunification.

France's then president Francois Mitterrand and Britain's prime minister Margaret Thatcher were both caught out by the speed with which the Germans remade their country in the wake of Communism's collapse.

While Thatcher's supporters would go on to portray her as the heroine of the West's victory in the Cold War, a victory symbolised by the Wall's collapse, at the time the prospect of German reunification "horrified" her.

And, while Mitterrand has been seen as a great friend and ally of Germany's then chancellor Helmut Kohl in the campaign for European integration, in 1989 he neither foresaw nor supported the re-integration of Germany.

"In 1989 we gave the impression of wavering in the face of history. Twenty years on, let's do it justice," said Pierre Lellouche, French European affairs minister, as he followed Britain in opening the 1989-90 diplomatic archive.

Given the subsequent success of the reunification project, and the warm ties that Paris in particular now has with Berlin, the files will make uncomfortable reading for some French and British political veterans.

"France and Great Britain should pull together today in the face of the German threat," Thatcher told the French ambassador to London in March 1990, according to a French diplomatic telegramme released for the anniversary.

"Kohl is capable of anything. He has become another man. He doesn't know himself any more. He sees himself as the master and is starting to act like it," she warned, according to the French translation of her remarks.

French historian Maurice Vaisse, who helped supervise the release of the files, said that Thatcher appeared "horrified" by the prospect that German reunification would make Berlin the dominant force in Europe.

According to the British archive, two months before the fall of the Wall, Thatcher told the Soviet leader Mikhail Gorbachev that "neither Britain nor Western Europe wanted the reunification of Germany.

"This would lead to a change to postwar borders, and we cannot allow that because such a development would undermine the stability of the whole international situation and could endanger our security," she said.

In effect, she was asking the Britain's former Cold War enemy to help her thwart German ambitions of one of the West's staunchest allies.

Mitterrand adviser Jacques Attali — who in another irony of fate would go on to head the European Bank of Reconstruction and Development set up to fund post Cold War reform in Eastern Europe — also opposed reunification.

The British archive records him meeting Gorbachev aide Vadim Zagladin in Kyiv one month after the wall came down and complaining that Russia had not intervened in East Germany to head off reunification moves.

"This has caused a fear approaching panic," he said, according the files.

Four months later, in April 1990 and with reunification imminent, Attali reportedly told Mitterrand that he would "fly off to live on Mars" if the inevitable happened.

Mitterrand and Thatcher also shared their concerns in person.

In January 1990, the French leader told his British counterpart at a Paris dinner that a united Germany could "make more ground than even Hitler had" according to a note by Thatcher aide Charles Powell.

Shortly after the fall of the wall, in December 1989 — when his foreign ministry was telling him reunification was "not a realistic possibility" — Mitterrand even visited East Germany's moribund Communist regime.

Trapped in a Cold War mentality, and mindful of their countries' suffering at the hands of a powerful Germany during World War II, the leaders of the day had difficulty envisaging such a rapid sea change in European politics.