SHADOW chancellor John McDonnell was warned today that his proposal for a “close” relationship with the European Union single market could block many Labour manifesto pledges from becoming reality.

He claimed that a Brexit deal involving a customs union that has a “close and collaborative” relationship with the single market would win a Commons majority and be backed by business.

Mr McDonnell warned that a no-deal Brexit would be “pretty catastrophic.”

Labour will support a deal that would “protect jobs and the economy,” he added.

Alex Gordon, convener of Lexit, the Left Leave coalition during the referendum two years ago, told the Star that the only deal the EU is committed to offer Ms May is one that would “neutralise” Labour’s pledges to renationalise rail, mail and energy.

He added: “After Monday’s disastrous Tory budget announcement, it is clearer than ever that British voters want a general election where they have a real choice between austerity under the Tories and reconstruction under Labour.

“The danger is that May’s Chequers deal will remove a future Labour government’s ability to offer British voters a real alternative.”

Communist Party of Britain general secretary Rob Griffiths said that access to the EU market on favourable terms would be beneficial but “not at the cost of signing up to the single market rules.”

He told the Star: “Signing up to the single market rules would obstruct a left-led Labour government from carrying out most of its manifesto policies.”

Mr Griffiths argued that all members of the World Trade Organisation have access to the single market, so signing up to its rules would not be worth it if Britain is not free to strike its own deals with other countries.