Activists voted overwhelmingly at the party’s annual conference in Bournemouth on Sunday to back leader Jo Swinson’s proposal to revoke the UK’s Article 50 letter informing Brussels of its intention to quit the EU.
But Lamb warned that there was a “real danger” of breaking the nation’s social contract if Leave-voters felt that their referendum victory in 2016 was simply being cast aside.
The former health minister, who is a member of the MPs For A Deal group calling for a new vote on the last version of Theresa May’s withdrawal agreement, warned his party that a failure to compromise was fuelling the rise of populist figures like Nigel Farage and Boris Johnson.
“I don’t feel personally that there are enough people out there trying to find ways to re-unite our country,” Sir Norman told BBC Radio 4’s Today programme.
“I think that the polarisation that we are seeing is incredibly dangerous. I think we are playing with fire in many ways.”
Lamb – who has said he will stand down as MP for Norfolk North at the next election – voted earlier this year for versions of Brexit which would have seen the UK leave the EU but remain within a customs union or in a Norway-style “common market 2.0” arrangement involving close trade links with the continent.
He said the refusal of other Remain-backing MPs to compromise at that point “opened the door to Nigel Farage and Boris Johnson to prosper”.
And he warned: “We have got to be very careful what we wish for. If we take this to the very limit in a situation where one side or the other is vanquished entirely, I think there is a real danger that we break the social contract inner country and I think we all have a responsibility to find ways to reunite the country in a common endeavour.”
The Lib Dems’ new policy will see the party seek a Final Say referendum on whether the UK should accept any Brexit outcome. But if an election comes before any referendum – as now seems likely – they will campaign on a platform of withdrawing the UK’s Article 50 letter if they win power.
In a testy exchange with presenter Piers Morgan on ITV1’s Good Morning Britain, Ms Swinson rejected accusations that the policy was undemocratic.
She was confronted with video footage of former Lib Dem leader Paddy Ashdown shortly before the 2016 result was announced, when he was apparently expecting a Remain victory, in which he said: “I will forgive no-one who does not accept the sovereign voice of the British people once it has spoken, whether it is by one per cent or by 25 per cent.”
Ms Swinson responded: “We had that referendum three and a half years ago and the government has gone away and taken the result of that referendum and negotiated what that will mean for the British public.
“What is on offer today bears no resemblance to what was said in the 2016 referendum campaign.
“We are still campaigning for a People’s Vote. We believe a referendum is the best way to get clarity, to get resolution of this current gridlock and Brexit impasse.
“But it does look like it may be that a general election will be upon us an in that general election – that democratic process – the Liberal Democrats will campaign to stop Brexit.”
Ms Swinson did not rule out campaigning to take the UK back into the EU if Brexit goes ahead, telling Today: “I’m not going to get into the hypothetical because I am absolutely focused and determined on stopping Brexit. That fight has not been lost.
“It is September, we are still members of the European Union. It is a membership that brings huge benefits for our economy, for the way in which we have improved workers’ rights, environmental protections, the way in which we engage around the world. I’m not going to throw that away. I’m not going to accept defeat on that. We are going to fight to stay in the EU.”