Sir John Major has attacked "Ultra-Brexiteers" within the Conservative Party accusing them of seeking to force a complete break with Europe.
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".
Writing in The Mail on Sunday, 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.
He 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.
"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," he wrote.
"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 by some Brexiteers that Britain could thrive under WTO rules, warning that 90% of UK exports to the EU would become more expensive, with tariffs that would add about £6 billion to their costs.
"It is worth reflecting that those who make such reassuring noises include the very same people who urged the UK to vote Leave on the basis that 'we will be able to give an extra £350 million a week to the NHS'; that 'nobody is talking about threatening our place in the single market'; and that 'there is no prospect of a second Scottish referendum'," he wrote.
"We already know that all three of the above - and much else - were fake facts and bogus promises.
"It was dishonest and wrong to promise the British people an easy, favourable deal with the EU, wrong to promise swift new trade deals, and wrong to state that the Irish peace process would not be unsettled by Brexit."
Additional reporting by the Press Association.