The former prime minister said that, having won the referendum last year with “fake facts and bogus promise”, the “ultras” were now shouting down anyone who expressed an opposing view in a way that was “totally un-British”.
He warned if Britain failed to strike a deal with the remaining EU member states and was forced to fall back on World Trade Organisation (WTO) rules – as some hardline Brexit supporters have advocated – it would be “disadvantageous in every way”.
Sir John did not name names, but his comments will be seen, at least in part, as being aimed at leading Leave campaigners such as Boris Johnson, Michael Gove, Iain Duncan Smith and Jacob Rees-Mogg.
Sir John said the “ultras” were lashing out with “vitriolic and personal attacks” because they were terrified their triumph of taking the country out of Europe would be snatched away and he urged other Brexit supporters to disown them. Writing in a Sunday newspaper, he said: “It is time for the minority of ‘ultra Brexiteers’ – those who believe in a complete break from Europe – to stop shouting down anyone with an opposing view.
“It is not only unattractive but profoundly undemocratic and totally un-British.
“Instead, they launch vitriolic and personal attacks on the governor of the Bank of England, judges, civil servants, foreign politicians and other public figures. In doing so, they demean both themselves and their cause.
“If the rancour merely came from rabble elements, or extreme minorities, it could be ignored. But when it comes from politicians, including those from within the governing party, it is time to confront it.”
Sir John also dismissed claims Britain could thrive under WTO rules.