Former Lib Dem minister Norman Lamb is considering resigning from the party whip because he fears it is becoming as uncompromising as the ERG.
Lamb was the only MP in his party to vote in favour of a customs union, with only one other (Tim Farron) joining him to vote for Common Market 2.0
He told the Eastern Daily Press that he could resign from the Lib Dem whip.
He said: ‘I’m thinking of whether I should resign from the whip, staying as a Liberal Democrat, but I feel so strongly about the need to heal divisions and bring people together. I was deeply unhappy with my colleagues’ unwillingness to participate in that process and to vote for options which I think would have helped bring the country together.’
But he later told BBC that he would ‘stick with my membership of the Lib Dems as long as I am allowed to stay.’
He added: ‘I don’t want us to be the mirror image of the ERG just stuck in a trench and not moving and that’s why I felt particularly distressed yesterday.’
Lamb has joined a cross-party effort to try to force Theresa May to stop no-deal Brexit by tabling a bill requiring her to extend the negotiation process beyond April 12.
It is supported by former Tory chair Dame Caroline Spelman, Commons Brexit Committee chair Hilary Benn and former attorney general Dominic Grieve and Liberal Democrat Norman Lamb.
The group hopes once it has passed the Commons it could be approved by the House of Lords and granted Royal Assent in time for the emergency EU summit on April 10.