A no-deal Brexit would be “national suicide”, Dominic Grieve has warned.

The former Conservative attorney general is leading efforts to avoid leaving the EU without a deal and is pushing for a second referendum.

MPs are expected to vote down Theresa May’s Brexit proposal when it is put to the Commons on Tuesday.

But if MPs cannot agree an alternative plan, the UK is set to leave the EU without a deal by default on March 29.

International trade secretary Liam Fox earlier this morning said a no-deal Brexit was not as bad as some claimed.

“I don’t regard no-deal as national suicide. This is not Dunkirk, this is leaving the European Union,” he told BBC Radio 4′s Today programme.

“I think no-deal would damage our economy – I’ve been frank about that – but I think it’s survivable.

“I think no Brexit, politically, is a disaster from which we might not recover.”

But speaking on the same programme, Grieve hit back at Fox. “It would be national suicide,” he said.

“It will lead to the break up of the UK for starters. That seems to me to be a pretty clear indication of a form of national suicide.

“The economic damage which it will do to us will be immense, so that the most vulnerable in our society will be those who suffer most as a consequence.”

Defence minister Tobias Ellwood has said he would resign from the government if it oversaw a no deal exit.

“I would not stay in office, I would stand in front of that no deal juggernaut,” he told BBC Radio 4′s Westminster Hour.

“It would be an irresponsible act of self-harm and from security reasons alone it would be damaging our international reputation as well. No deal for me is simply not plausible.”

In an effort to convince pro-Brexit Tory MPs to vote for her deal, May will use a speech this morning to warn parliament is more likely to block Brexit than allow the UK to crash out of the EU without a deal.

She will warn that trust in politicians will suffer “catastrophic harm” if MPs fail to implement the result of the referendum.

Boris Johnson also told LBC this morning that any parliamentary moves to try and thwart or frustrate Brexit would be seen as a betrayal.

“I notice all this stuff about complicated jiggery-pokery for Parliament to frustrate the deal,” he said. “I don’t think that really can be done. I think that we are really playing with fire.”