Sir John Major has told ITV News the Conservative rebels Theresa May is facing over her Brexit plan are more "hardline" and "entrenched" than the Tory MPs who defied him over Europe in the 1990s.
The former Prime Minister said a group of Brexiters within the Tory party - led by Jacob Rees-Mogg - are "very difficult to negotiate with" and give Mrs May "rather threatening lectures day after day as to what they will expect [over Brexit], when they are actually a minority in the Conservative parliamentary party", adding some are "fanatics" who are "prepared to go to almost any lengths to ensure we leave Europe".
The rebels' behaviour could "cause a Corbyn government" and lead to a general election this autumn or next spring, he believes.
Speaking to ITV News Political Editor Robert Peston in the latest episode of his new online series Now What?, Sir John said:
There is 'undoubtedly' a case for a second referendum' on Brexit
A Brexit 'no deal' scenario would be 'catastrophic' and likely lead to a general election
Brexit voters were made false promises by campaigners and will become worse off, not better off
Watch the full episode of Now What? with Sir John Major here
Since Theresa May agreed her Brexit plan with her Cabinet in Chequers on 6 July, Brexit Secretary David Davis and Foreign Secretary Boris Johnson have resigned from government over its contents. Several government ministers have also quit.
On Monday, Theresa May bowed to pressure from Tory Brexiters after accepting crucial changes to plans for leaving the European Union - narrowly winning a Commons vote by 305 votes to 302
The European Research Group, a Eurosceptic group of Tory MPs which include Jacob Rees-Mogg, Sir Bernard Jenkin, Priti Patel and Iain Duncan Smith, tabled four amendments to the Government's Customs Bill aimed at imposing strict conditions on the Prime Minister after she produced a plan at Chequers that would keep the UK closely tied to Brussels' rules on goods and food.
Sir John, who was Prime Minister between 1990 and 1997, faced a rebellion from within his party over Europe when he was in power. He was defeated in a Commons vote over the UK implementing the Maastricht Treaty, which created the European Union.
Referring to the American conservative political movement, Sir John said: "There is a bit of a Tea Party grouping within the hardline European Research Group and that makes it very difficult to negotiate with them. I think it must be very hard for the Prime Minister to take rather threatening lectures day after day as to what they will expect, when they are actually a minority in the Conservative parliamentary party"
'Case for a second referendum'
There is 'undoubtedly a case for a second EU referendum, Sir John said, because people voted on an 'entirely false prospectus' where the vast majority of promises made by campaigners are 'pie in the sky' and 'simply not going to happen'.
"At some stage, the public will learn that they are not going to happen and they will then, I think, be a terrible backlash against those people who made promises and forced through a Brexit and then people found that they were worse off, not better off", said the former PM, who backed Remain during the referendum campaign.
On Sunday, former Conservative cabinet minister Justine Greening said there should be a second referendum, with three options on the ballot paper - Theresa May's plan, Brexit with "no deal" or remaining in the EU.
'No Brexit deal could force a general election'
Sir John said there could be a number of situations where a general election could be forced - including a scenario where no deal is reached over Brexit.
"If we move forward in a way - that at the moment it seems to me we are beginning to head - which is towards a negotiation that ends up with no deal because whatever the Prime Minister puts forward is voted down in Parliament...it is difficult to see how a general election can be avoided and difficult to see how an election for Prime Minister can be avoided.
If the hard, most convinced Brexit supporters continue to say there is compromise, whatever is put forward is going to be rejected, then that is a route in which we are headed and it would be disastrous for the UK."
Responding to the decision on Tuesday by the Electoral Commission to fine Brexit campaign group Vote Leave for breaking electoral law over spending during the referendum campaign, the former PM said he doesn't know whether it will have changed the result, but what was more of an issue was the electorate was made 'undeliverable promises'.
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