The ex-Lib Dem leader said “people’s opinions change” and halting Brexit despite 17 million Leave votes last June must be considered.
He made the claim to the BBC’s Emily Maitlis this evening as he promoted his new book “How to stop Brexit”.
Mr Clegg told an audience at the University of London: “Democracies are living breathing things, and things change, people’s opinions change – that’s why we have elections all the time.
“The whole point of a democracy, as David Davis said, and I’ve put it at the front of my book: ‘If a democracy is not able to change its mind, it then ceases to be a democracy.’”
Mr Clegg said the Leave campaign had promised voters £350million for the NHS, new trade deals, total control of Britain’s borders, and economic success as we became “Global Britain”.
He said he did not believe David Davis will deliver on any of this.
Mr Clegg said: “People voted for Brexit in good faith, because they were promised it would be a good thing bringing all sorts of bounty to them and their families.
“I think it is highly predictable that none of it, none of it will actually be translated into the deal put before parliament.
Nick Clegg believes it’s democratic to try to reverse Brexit
“In a democracy it is right for our MPs to say: ‘Thank you David Davis, thank you Theresa May, but going on what my constituents were promised and what’s in this deal, since you have not delivered anything my constituents expected, I am going to withhold consent for it.’
“That’s my fundamental democratic argument.”
Moderating, Ms Maitlis asked Mr Clegg whether he was saying he would not have written his book on blocking Brexit if he felt negotiations were going differently.
He admitted he would still hold the belief that Brexit was not the right decision for the country.
Clegg said MPs would be within their rights to reject David Davis and Michel Barnier’s deal
Clegg branded the £350million a week for the NHS a ‘lie’
He said: “I think the fundamental flaw was that the promises that were made were almost entirely fictional and they knew it.
“They knew it, that’s what makes me so angry. They lied to the British people and they knew it.
“If you see what Dominic Cummings and people like that have written, they have said: ‘We do not think we would have won this if we had not made the commitment of £350million extra for the NHS every week.’
“This is something you can easily pull apart, but they repeated it.
Clegg was promoting his new book ‘How to stop Brexit’
“The reason they made those false claims, by the way, is because they thought they would get away with it. Because in a referendum they thought: ‘Well it doesn’t matter what I say, because the truth will never catch up with me.’
“I think that is outrageous.”
He added: “In a democracy, you shouldn’t just get away with stuff like that. You have to be held to account, if you don’t come up with what you’ve said you would.
“I think it’s a negation of democracy, what’s going on at the moment.”