Politicians have a duty to prevent the country committing national suicide in relation to Brexit, a pro-EU Conservative MP has said.

Former attorney general Dominic Grieve told a packed hall that once Prime Minister Theresa May’s deal is defeated in the Commons next week the only option is a second referendum.

He also said that Conservatives had “blown it” by letting a “revolutionary change take place in the name of tradition”.

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Dominic Grieve spoke during a convention on a second EU referendum in central London (Stefan Rousseau/PA)

The MP for Beaconsfield was speaking at an “emergency convention” on a second EU referendum at Emmanuel Centre in Westminster on Friday.

Mr Grieve said that if MPs vote against Mrs May’s deal as is predicted next week, then the only option is to go back to the British public and hold a second referendum.

He added: “My friend the Prime Minister has been doing her very best to try to find a way out of this problem that minimises the damage while trying to honour the referendum result.

“The unpleasant truth for her is that it can satisfy no one.

“There is only one way out. When the PM’s deal is defeated, what else can we possibly offer to the British public which has any chance at all, but to go back to ask them to reconsider their decision.

“Parliamentarians do have some duties and one of them is to prevent people from committing national suicide.”

Mr Grieve received a standing ovation from the packed hall when he stepped on stage and again when he finished speaking.

He told the audience that options such as a Norway-style deal or customs union with the EU just “brush problems under the carpet” and the only option was to go back to the public.

But Mr Grieve did not say what questions should be on a second referendum or whether a no-deal Brexit should be on the ballot paper.

Mr Grieve said he had told sixth form students that what it meant to be a conservative was to believe in principals of “continuity” and “pragmatism” and to try to avoid “revolutionary changes”.

Mr Grieve added: “I then explained to them that we had blown it because we allowed a revolutionary change to take place in the name of tradition, and such things can never work.

“It ends up where you do not want to be.”

Former Green Party leader Caroline Lucas told the audience the referendum of 2016 had highlighted the problems at the heart of British democracy which can no longer be ignored.

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Caroline Lucas: ‘The lie at the heart of the leave campaign was that this downward spiral could be reversed by leaving the EU’ (Stefan Rousseau/PA)

The Brighton Pavilion MP said people voted with a “collective howl of rage” but it was also a collective message that the status quo was “intolerable”.

Ms Lucas added: “People were and are angry for many reasons, a general sense that any change is better than the status quo, that they have nothing left to lose. The tragedy of course is they do and likely will.

“We must also be very honest, we know that immigration has been a good thing for Britain.

“The point is that its benefits have not been equally shared and big changes to our communities can be frightening.

“The tragedy is of course is that Brexit would make it harder to address all of those concerns.”

Ms Lucas said a second referendum could “fire the starting gun” on a new conversation about how the country is governed.

She called for a new social contract, better jobs and green investment to address the “grotesque inequalities” and proposed introducing proportional representation to replace the first-past-the-post voting system.

She added: “The lie at the heart of the leave campaign was that this downward spiral could be reversed by leaving the EU.

“The serious democratic deficit in our own country, Brexit has laid bare the extent to which our government structures are derelict.

“A people’s vote should be the starting gun on the race to genuinely democratise the UK.”

Musician Jarvis Cocker said the UK pop charts could shed a light on Brexit.

He told the audience that new and challenging ideas could get to number one if enough people liked them.

But Cocker said that, in the 1990s, singles began being sold at a discounted rate when they were first released, meaning they often rose quickly to number one before later dropping out of the charts.

He added: “That term ‘pop’ has become something like a dirty word, but I’m talking about good pop as in ‘popular’ as opposed to bad pop as in ‘populism’.

“New and challenging ideas could rise to the top if enough people decided to put them there by buying the records. It was proper democracy.

“Some time in 1996 someone came up with the idea of selling singles at a discount price on the first day of release.

“All sense of narrative disappeared overnight and the general public’s interest waned almost instantly. That is the moment when good pop became bad pop.”

The former Pulp frontman said the Brexit win for Leave in the referendum was the equivalent of a single entering the top 40 charts at number 19.

He added: “It’s hardly setting the charts alight, we would not have dared to call it a hit back in the day.

“We definitely would not have dared to call it the will of the people, so why is the result being presented as one?

“So let’s do it again, let’s have a second referendum and let’s define the margin of victory and put this nightmare behind us and move on to thinking about something more interesting – like dancing – instead.”

Labour MP Stella Creasy called for a citizen’s assembly to decide on Brexit, including what questions could be in a second referendum.

She said: “One of the challenges we have in finding a way forward is finding a way as a country to be able to talk about difficult issues, to actually be able to find a way to resolve it.

“How we get to that second referendum will define the outcome.”

Pro-European Labour peer Lord Andrew Adonis said 16 and 17-year-olds should be allowed to vote in a new Brexit referendum and registered automatically.

Speaking to an audience of remainers in west London Lord Adonis said mobilising the younger generation would be crucial to winning a fresh referendum.

But he also stressed any remain campaign should not apologise for the EU.

He added: “We have got to have a profoundly, passionately, committed pro-European campaign. We shouldn’t be apologising for the very organisation we want to be a part of.

“We have to be much more passionate about staying in the EU.”

He said any people’s vote should be held during term time to make it easier for young people to vote, instead of the end of June when they are away on holiday or not at university.

Lord Adonis added: “It seems absolutely vital that the referendum is held during school and university term so that young people can vote easily.

“We should give the vote to 16 and 17-year-olds in this referendum and we should automatically register young people at their place of study.”

But he agreed with Paul Hilder, co-founder of Crowdpac with former Tory political adviser Steve Hilton, that any future remain campaigner must combat the leave slogans.

Lord Adonis said: “We have got to have an answer to the three Farage slogans – leave means leave; tell them again; and just get on with it.

“We have got to have a big and compelling message this time, save Britain from Brexit.”