Labour has vowed that a cross-party alliance of MPs will stop Theresa May crashing Britain out of the EU without a deal.

John McDonnell, the Shadow Chancellor, said there were “enough sensible people in the House of Commons” to prevent the growing risk of a no-agreement exit.

He said Labour would “put aside party interest” to strike alliances with MPs in other parties that would force the Government to “come to their senses”.

A key amendment has already been tabled, in part by former Tory Chancellor Kenneth Clarke, to give Parliament the ability to veto a “no deal” – or even a “bad deal” – outcome.

It demands that the Prime Minister’s plan for a two-year transition period is written into the EU Withdrawal Bill, preventing Brexit if that transition is not agreed.

Speaking on the BBC’s Andrew Marr programme, Mr McDonnell said, of the no-deal scenario: “I’m not willing to countenance that. I don’t think there is a majority in Parliament for no deal.

He attacked the Government for being “more interested in negotiating to save the Tory party than in the interests of the country ... it’s a disgrace.”

“I think there are enough sensible people in the House of Commons to say, ‘This cannot happen, we cannot damage our country in this way’.”

Several ex-Conservative ministers, together with SNP, Liberal Democrat and Green MPs, have already signed the crucial amendment to the EU Withdrawal Bill.

The 10 Democratic Unionist Party MPs propping up the Prime Minister in No 10 have ruled out a no-deal outcome, because it would mean the return of a hard Irish border.

It means continuing to pursue crashing out of the EU would threaten the deal that allowed Ms May to survive her election debacle.

A separate amendment, signed by 10 Tory MPs, says any final deal must be approved by an entirely separate act of Parliament, to give soft Brexit supporters more muscle.

But Chris Grayling, the Transport Secretary, accused Mr McDonnell of talking “complete nonsense”, insisting the path out of the EU was sealed when Article 50 was triggered.

“Parliament has already voted for leaving the European Union overwhelmingly,” he told the same programme.

Mr Grayling insisted a permanent collapse of the negotiations would punish the EU and that “Britain will succeed whatever happens”.

The Transport Secretary also said there was “not the remotest danger” that flights with the EU would be grounded if there was no deal – and argued it would help Britain grow more of its own food.

Last week the Prime Minister said Britain was starting to prepare for no deal, as the Brussels talks remain deadlocked, including by planning huge lorry parks to cope with new customs checks.