Sir John said Brexit is "probably today at its lowest level of popularity since June 2016", when 52% of Brits backed leave.

He said: "Despite the fact the opposition parties - leaving aside the SNP - don't want to talk about Brexit, within the public the debate is still there.

"At the moment, it looks as though the 2016 referendum is going to be as unsuccessful as the 1975 one was in proving to be a permanent settlement of this debate.

"We are as a country divided down the middle on this subject and it looks as though we are going to continue to be so for the foreseeable future."

Growing support for the EU was apparent when the lorry driver shortage caused chaos last year and the Government had to take measures to bolster the number of HGV operators.

Shortages had been put down to the number of European drivers heading back to the continent.

Post-pandemic problems like the cost of living crisis, rising energy bills and inflation have further added to growing regret for Brexit – although these have been seen across Europe, too.

In other findings, Sir John said it will be "extremely difficult" for the Tories to win the next election.

"No government that has presided over a financial crisis has eventually survived at the ballot box. Voters don't forget governments being forced to do a U-turn by the financial markets," he told reporters.

With the Tories trailing Labour by 25 points in the polls, he believes Labour has a "half decent chance" of winning a majority.

Rishi Sunak has slightly recovered from the depths the party plummeted to under Liz Truss, who spent a disastrous few weeks at No10.

The Conservatives had trailed Labour by more than 30 points under her, which could have translated to fewer than 60 seats at an election.

"I think arguably this is as bad as it ever was for a government," Sir John said.