Civil servants and politicians who are dealing "directly" with Brexit are "horrified" at the potential for a "disastrous" outcome to negotiations with the European Union, Sir Vince Cable has claimed.
The Liberal Democrat leader said they realise the UK does not have a strong hand in the talks and are "worried about the future of the country".
The former business secretary spoke as thousands of demonstrators joined the anti-Brexit People's March for Europe through central London, which will end with a rally in Parliament Square.
Before addressing Lib Dem activists who are joining the march, Sir Vince told the Press Association: "I think a lot of the people who are dealing with it directly and who don't necessarily have a political axe to grind are pretty horrified actually because they see the potential for disastrous negotiations, they realise Britain doesn't have a very strong hand in these negotiations and they are worried about the future of the country, as I am, as these people are."
Asked who exactly he was talking about, Sir Vince replied: "I'm talking about people in the other political parties, they go along with Brexit because they say, well people in my constituency voted for it, but deep down they are really, really worried about the consequences, and of course people who are not political."
Sir Vince's comments came at a critical moment for Brexit, with MPs set to vote on the repeal bill, formally known as the EU (Withdrawal) Bill, on Monday for the first time, and amid concerns over the progress of negotiations.
Foreign Secretary Boris Johnson on Friday made clear the Government's urgent wish to negotiate trade now, suggesting Article 50 sets out a legal duty to discuss the future relationship concurrently with withdrawal issues including citizens' rights, a financial settlement and the Irish border.
But he spoke after senior European figures, including EU chief negotiator Michel Barnier, voiced scepticism that talks would move on to trade relations by October, as hoped, as they have so far failed to deliver "decisive" progress on withdrawal issues.
Meanwhile, Theresa May was forced to rule out sacking ministers or aides suggested to be involved with a letter signed by between 30 and 40 Tory MPs which set out demands for what was seen as a "hard" Brexit that differed with Government policy.
Sir Vince said there is now a "swelling" of people who are "deeply alarmed" about where negotiations are heading and the "confusion and disunity" in the Government.
Public opinion will shift as more businesses hold back investment and "high quality" EU citizens join an "exodus" out of the country, he said.
"We've already seen the big devaluation (of the pound), and that had has quite a significant impact on people's living standards," Sir Vince said.
"There's already plenty of evidence that companies are not investing at the moment. They are holding back because of the uncertainty, and those that depend on the single market, the customs union obviously are going to hold back, that's very understandable.
"You are beginning to see more and more evidence of an exodus of high-quality, highly trained people from the European Union because of uncertainty about the future, all of these things are happening now and this is just the beginning."