Only a fool believes the political landscape will never change. As the Labour Prime Minister Jim Callaghan once told his aides: ‘There are times, perhaps once every 30 years, when there is a sea-change in politics. It then does not matter what you say or what you do. There is a shift in what the public wants and what it approves of.’

As it happens, Callaghan said those words almost exactly four decades ago, as he was preparing to lose the 1979 election to Margaret Thatcher.