A former cabinet minister has said Theresa May is heading for a "dead end" in the Brexit talks, which can only be solved by a fresh referendum.
Dominic Grieve, an ex-attorney general, said the prime minister's deal "looks pretty second rate" and the Brexit being delivered is something "very few people want".
The influential Tory MP will be among thousands of protestors descending on London on Saturday for what is being billed a the largest anti-Brexit demonstration to date, with more than 100,000 activists expected.
It comes as Ms May appealed to business leaders to help her secure a deal by spelling out the impact of a no-deal Brexit, after a difficult week where a key EU summit broke up without an agreement.
The Independent has learned that the prime minister used a conference call with 130 company bosses on Friday to offer a contrast between her plan and a chaotic exit from the EU - something that has been branded a "false choice" by critics as it removes the option of a fresh referendum.
Mr Grieve told BBC Radio 4's Today programme: "If we don’t do this now then we will lose the opportunity and once we are out of the EU on March 29, going back in is a completely different thing to deciding to stay in.
“My view has grown over the last few months that in fact we are reaching a dead end and that there may be some sort of deal on offer but one that i have to say looks to me pretty second rate.
“When you get this sort of problem, in view of the first referendum, the only solution is to go back to the public and say is this what you really want. And if they do want it, so be it.”
He said the previous referendum was based on an “abstract discussion”, adding: "I think this is the end. If people find that what they are about to get is what they want then I as a democrat would accept it.
"But what worries me is I think we are about to deliver a Brexit that I think, in fact, very few people want."
Ms May faced a major Tory backlash after she signalled that she would consider extending the transition to allow more time for UK and EU negotiators to hammer out problems around the future relationship, including the vexed issue of the Irish border.
Mr Grieve, who leads a band of pro-EU Tory rebels, said it was likely that the transition period would be “extended well beyond three years as we try to thrash out the continuing relationship”.
He added: "That highlights for me why in fact we are embarked on the project which is totally different from what people might have had any reason to expect in 2016.
"We are in the most extraordinary situation where we remain tied to all of the rules of the EU without any ability to influence the input.”
Mr Grieve also condemned Ms May for appearing to go back on her pledge to offer MPs a meaningful vote on any Brexit deal, saying their plans were “utterly flawed”.
His intervention came after the prime minister told businesses that time is running out to reach a Brexit deal, but she was confident it can be done.
Downing Street said Ms May told the business leaders that "significant progress" has been made in the talks.
"She acknowledged that there were a few significant issues that were still outstanding, but said that the very real sense she had from leaders around the table at the council was that they wanted to reach a deal as soon as possible this autumn," a No 10 spokesman said.
More than 100,000 people are expected to join the People's Vote demonstration in London, organised with The Independent, which will see politicians, activists and celebrities march from Park Lane to Parliament Square from midday.
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