Brexit has been compared by a leading Remain supporter to appeasement of Nazi Germany in the 1930s.
Former foreign office minister Lord Malloch-Brown, head of the Best for Britain group, made the comments after billionaire George Soros announced a campaign for a new Brexit referendum is set to be launched.
Mr Soros - who is reported to have given about £500,000 to Best for Britain, which was set up last year by anti-Brexit campaigner Gina Miller - said action was needed as EU withdrawal was "immensely damaging" for the UK.
Lord Malloch-Brown said Britain needed to stay close to the EU because instances like appeasement showed what happened when the UK tried to shut itself off from the continent.
He told BBC Radio 4's Today programme: "Britain's history as an island nation adjacent to mainland Europe is when we try to, sort of, pull away from Europe's problems and close ourselves off to them they have a horrible habit of infecting us anyway.
"Appeasement in the 1930s, you name it. For centuries Britain has ignored events on continental Europe at its peril."
He said Mr Soros's reputation as the "man who broke the Bank of England" in 1992, when the financier bet against sterling on the money markets, was an "unrelated issue" to the anti-Brexit push.
"He broke the Bank of England as a financier because the British pound was over-extended. It wasn't credible. He broke the pound, not the Bank of England, I should say.
"He is someone who has devoted decades to an extraordinary global philanthropy which has fought for democracy and open values."
Best for Britain, which wants to keep the UK open to EU membership, is expected to publish its campaign manifesto calling for a second referendum on June 8.