Justine Greening, who resigned as education secretary after Theresa May tried to move her in a reshuffle in January, said the European Research Group (ERG) of Tory MPs needs to face reality.
It comes after the 60-strong ERG issued an ultimatum to the Prime Minister over the EU’s customs union.
But Ms Greening, who backed Remain in the 2016 Brexit referendum, told Sky News there needs to be give and take and no one side will get absolutely everything it wants in the negotiations.
When asked if too much attention was being given to the ERG, Ms Greening said: “Well look, I think what we can’t have is a group of MPs who behave a little bit like Russia does on the Security Council – vetoing things that they don’t like.
“We have got to go forward on Brexit as a country together.
“That will mean give and take and people need to understand that, whatever wing of my party they are on, and whatever elements of the Leave/Remain debate they are on.
“I’m afraid no one is going to quite get their perfect outcome.
“The sooner they all realise that and then work through the give and take and find a sustainable long-term solution on Brexit, the sooner we’ll be able to get on with the implementation planning around that which is urgent, and the sooner we’ll be able to get on with running the country and get on with the domestic agenda – for me the equality of opportunity – and the issues that are really at the heart of what I think people want tackled.”
Mrs May has been steadfast in her stance that there will be no customs union post-Brexit, but she is struggling to reconcile the demands of warring Brexiteers and Remainers and avoid more Cabinet resignations.
She also faces near-civil war on her backbenches, with pro-Remain Tory rebels threatening to vote with Labour and other opposition parties in the Commons to stay in the customs union.
The so-called “Brexit war cabinet” of senior ministers met on Wednesday to try to reach a deal on whether the UK should leave Europe’s customs union, enter a “customs partnership” or adopt an approach of “maximum facilitation”.
But a decision on future customs arrangements was put off after the crunch meeting failed to reach an agreement.
There are reports the “war cabinet” is against Mrs May’s preferred option of a customs partnership.
Ms Greening said she was concerned the committee will out-vote the PM on the issue, adding it is “out of step” with the parliamentary party as a whole.
“I think it’s time for the moderates in the party like myself to work with the Prime Minister on a sensible approach to the customs policy and a broader package and then make sure this is something we can get through Parliament,” she said.
But staunch Leave supporter Jacob Rees-Mogg told Sky News: “I have no authority to veto anything. I’m a backbench Tory MP. The Conservative manifesto said that we would leave the customs union and we would leave the single market. I believe that politicians should implement the promises that they’ve given in manifestos.
“So all I’ve been doing – and other members of the European Research Group have been doing – is encouraging the Government to stick to the promises it has made and the Prime Minister Theresa May has made very clear in her various speeches, whether it’s the Lancaster House, Florence or Mansion House speech.
“So we are very consistent with Government policy, we are supporting the Government implementing its policy in the face of a lot of opposition from other sources, particularly at the moment the House of Lords.”
He added that it would be “bizarre to think she would retreat from that promise [leaving the customs union]” and that he “doesn’t think she’s going to”.