Sir John Major has launched a scathing attack on "ultra Brexiteers" inside the Conservative Party, saying they want to force a complete break with Europe.
The former prime minister said that having won the referendum with "fake facts and bogus promise", the "ultras" were now shouting down any opposing views in a "totally un-British" way.
Writing in The Mail on Sunday, he warned that if Britain failed to agree a deal with the EU, it would be "disadvantageous in every way".
Sir John did not name anyone, but his comments may be perceived as being aimed at leading Leave campaigners like Michael Gove, Boris Johnson, Iain Duncan Smith and Jacob Rees-Mogg.
He said the "ultras" were lashing out with "vitriolic and personal attacks" because they were scared that their win will be taken away from them, 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."
He also dismissed claims by Brexiteers that Britain could thrive under World Trade Organisation rules, warning that 90% of UK exports to the EU would become more expensive, with tariffs adding 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."