The Queen expressed support for EU integration at a historic meeting with German diplomats, a declassified account of a meeting shows.

A diplomatic cable written by Ambassador Rüdiger Freiherr von Wechmar after a meeting with the monarch in 1988 says that the Queen left “no doubt that the future of Britain lies in Europe”.

The ambassador spoke with Elizabeth II for a farewell meeting at the German embassy in London and relayed his conversation back to his government.

The account of the meeting, reported by German’s Der Spiegel outlet, sheds light on the private views of the monarch, who has made an effort to keep out of politics throughout her reign – including in the Brexit debate.

There have long been rumours that the Queen privately supports European integration: she raised eyebrows at the state opening of Parliament in 2017 – the first after the referendum – when she turned up wearing a blue jacket and hat with yellow flowers in a pattern resembling the EU flag.

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Elizabeth is said to have told the outgoing ambassador that “some have not realised” yet that the UK belongs in Europe – referring to her subjects.

According to the account, she is said to have noted that many British people did not yet have an understanding of the single market, and said it was “about time” for a government education campaign to explain the union to voters.

The account also suggests the monarch was highly critical of then prime minister Margaret Thatcher. When the ambassador suggested that Ms Thatcher seemed to want a different kind of European integration to the one supported by the then German government, the Monarch is said to have replied: “That will change.” After a pause, she added: “If she is still around.”

Discussing Ms Thatcher’s ability to adapt to new political circumstances, the Queen is said to have replied: “Yes, even she has now discovered the hole in the ozone layer.”