Britain’s politicians have long been scared of Brexit. At the last general election, Labour made it clear that it did not want to reopen the national debate on membership of the EU. The UK would stay out of the customs union and single market, Sir Keir Starmer vowed – a striking promise from a man who was a key mover in the push for a second referendum. Not even the Liberal Democrats promised to take Britain back into the bloc, scarred by the “b…