Exasperated British diplomats warned that Margaret Thatcher’s reservations about German reunification had caused “growing resentment” among Germans, according to newly declassified documents that shed light on a loss of influence in Europe predating current rifts over Brexit.

By February 1990, months before reunification, the standing of the UK in Germany was “at its lowest for years”, the Foreign Office was warned by the British ambassador to West Germany, Christopher Mallaby.

While Thatcher’s opposition to the two German states uniting has long been known, the files released on Wednesday at the National Archives in Kew detail the extent to which her position caused divisions with her diplomats, among others.

One file notes that Douglas Hurd, then the foreign secretary, thought Britain should be very cautious “not to appear to be a brake on everything” and “should come forward with some positive ideas of [its] own”.

German reunification: together into the great unknown - archive, October 1990 Read more

On the eve of reunification, which took place on 3 October 1990, a joint dispatch by the British ambassadors to East and West Germany forecast “the likely nature and aspirations” of the new united country.

“Germany is again in the ascendant. With the scars of 1933-45 still vivid in many memories, this has not surprisingly caused concern in other parts of Europe,” stated the dispatch from Patrick Eyers, the ambassador to East Germany, and Mallaby.

“Twice bitten, thrice vigilant. Germany’s neighbours naturally wonder how far the Germans have really changed since 1945, and whether following unification there will be another shift in the behaviour of a nation that so often has proved volatile. What will sovereign united Germany be like?”

Mallaby and Eyers concluded: “There is no reason to expect reversion to the behaviour which caused two world wars.”

But they added: “Our German ally and partner will be much more difficult but not dangerous to deal with. We shall need in particular to watch out for interaction between greater German assertiveness and pressure from German public over defence policy, which could cause serious problems.”

Problems of a different kind had already been stored up, however, as a result of Thatcher’s stance. It later transpired she had told the Soviet leader, Mikhail Gorbachev, that Britain and western Europe were not interested in the unification of Germany.

The documents released from Kew include a February 1990 dispatch from Pauline Neville-Jones, a diplomat then stationed at the British embassy in Bonn, who noted how Thatcher’s attitude to German reunification was attracting widespread criticism in the West German media. “The tone is deplorable. But damage is being done,” she said.

In a final dispatch from Eyers in which he bade “farewell to an unloved country,” Britain’s man in East Germany wrote on 2 October 1990: “At midnight tonight the German Democratic Republic will cease to exist as a state.

“In what mood do the people of the GDR come to unity? … My impression is one of deep emotion, of contentment mixed with a certain trepidation in the face of the uncertainties ahead. But none of them is looking back.”

Mallaby meanwhile was raising a glass to Germany over lunch, where he told those gathered around him: “Long live reunified Berlin in a sovereign Germany, in an undivided Europe.”