Labour would almost certainly seek a vote of no confidence in Theresa May’s government if she loses the key Commons vote on her Brexit deal in nine days’ time, Keir Starmer has said.

Setting out the likely choreography for opposition efforts if, as expected, May is defeated on 11 December, the shadow Brexit secretary said it seemed impossible that May could remain in office if she was defeated on her flagship policy.

“I think the prime minister, as we all know, is going to struggle between now and that vote,” Starmer told Sky’s Sophy Ridge on Sunday show, saying that if she were to lose, May would have to outline her next move to the Commons.

“We need to see what that is. But it seems to me that if the prime minister has lost a vote of that sort of significance, then there has to be a question of confidence in her government,” he said. “I think it’s inevitable that we will seek to move that.

“Obviously, it’ll depend on what actually happens in nine days. It depends on what the response is. But if she’s lost a vote of this significance after two years of negotiation, then it is right that there should be a general election because, but for the Fixed-term Parliaments Act, the convention was always, if a government loses what’s called a confidence vote – something of such significance – then that government has to go.”

Labour’s policy has long been to push for a general election if no Brexit deal can be reached, but Starmer’s comments firm up the likely timetable. If May’s government were not deposed, he said, Labour would start seeking a second referendum.

“Obviously, if that doesn’t happen, we need to press on to other options such as a public vote because, having gone through the first two options, we would need to look at what happens then,” he said.

The likelihood of the party pushing for a new Brexit referendum has appeared to grow over time. Last week the shadow chancellor, John McDonnell, said Labour would “inevitably” back a second referendum if the party was unable to force a general election.

Asked about those comments, Starmer said: “John is going through exactly the same process as me – if a general election is not possible, then options such as a public vote will have to be looked at.”

If this took place, Starmer added, the vote should not include the option of a no-deal departure from the EU, as this would be too damaging for the UK.

“I don’t actually think that this prime minister will move to a no-deal situation,” he said. “She knows the risks. She’s very serious about counter-terrorism and security. I don’t think, when she stands up if she loses this vote, that she’s likely to say: ‘I’m now going to take the country off the cliff. I’m going to go for the no-deal scenario.’”

This was, however, later contradicted by Labour’s shadow international trade secretary, Barry Gardiner. Quizzed on BBC One’s Andrew Marr show about the idea of a second referendum, Gardiner said that if this happened, “remain and, I think, no-deal would both be on the table”.

From no confidence to no deal, the choice for MPs should May’s plan fail Read more

Speaking later on the Ridge show, the Conservative party chair, Brandon Lewis, again urged MPs to back May’s deal, saying there was no plan B.

“Well actually, plan B is plan A – to get this deal agreed. It is the only deal that’s there on the table. It’s the only option we have got. If this deal doesn’t go through we have the risk of no Brexit, no deal potentially,” he said.