Labour’s alternative Brexit plan could prevent a political vacuum engulfing Westminster if Theresa May’s withdrawal deal is defeated next week, the shadow chancellor said.

John McDonnell said the Prime Minister’s plan appeared “dead in the water” – but said the proposals being put forward by Labour could “give a level of certainty” for the next stage of the Brexit negotiations.

Speaking on a campaign visit to Scotland, Mr McDonnell said Labour’s alternative – which includes a permanent customs union, the UK having a “close and collaborative” relationship with the single market and the continued protection of employment, consumer and environmental rights – was a “decent compromise”.

He insisted they could provide a way forward if MPs in the Commons vote against Mrs May on Tuesday.

He criticised the Government for “wasting time” debating the withdrawal plan from the European Union that Mrs May has negotiated, saying: “It looks as though it is dead in the water.

“We’ve been saying over the last week the Prime Minister should recognise that and stop wasting the time of Parliament, and let’s just get on with working on where we go from here.

“Here’s our proposal, we think it’s a way forward to get a negotiated settlement which accepts the referendum result but gives us a deal that will protect jobs and the economy, let’s get on with the negotiations around that with our European partners.”

Mr McDonnell, who spoke to journalists during a visit to Airdrie, North Lanarkshire, insisted: “The Government should move to one side and let us get on with that, or failing that let’s have a general election.”

If there was no prospect of that, he said Labour would support a People’s Vote, although he was sceptical about whether Mrs May’s proposals should be put to the public if they are rejected by the House of Commons.

“If it can’t get a majority in parliament, I can’t see how it can then be put to the people,” he said.

“She might (want to do that) but whether parliament would after having killed it off already, it is impossible to say.”

He insisted: “If the vote goes against the Prime Minister’s deal, that’s when parliamentarians have to have a serious consideration of other options and I think our option could command support.”

The Labour MP added: “All the focus has been on the government proposals, now if they get defeated on Tuesday there is a vacuum there that I think we can fill and that I think will be an opportunity for a more constructive debate about the alternatives.”

He continued: “I think our European partners, they have reluctantly signed up to Theresa May’s deal because they thought maybe that would get through, it was the only thing that would fly. It clearly isn’t, so that’s why I think they would be open to a constructive renegotiation.”

Mr McDonnell went on: “There isn’t a majority for Theresa May’s deal, as far as I can see, secondly there is an overwhelming majority in Parliament against no deal.

“We’ve got to give certainty and reassurance to people, that includes the markets and other, and one way of doing that is having a serious discussion about alternatives, and our alternative is there and could provide that certainty.

“That’s the message we will be putting out, here is an alternative that could give a level of certainty about the next stage of the negotiations that could steady the markets.”