Jeremy Corbyn has failed to rule out a second EU referendum if he becomes Prime Minister.

The Labour leader said his party was “not advocating” another vote on EU membership, but stopped short of ruling it out altogether.

It came as the SNP invited Labour to join forces with other opposition parties to keep Britain in the single market and customs union.

Ian Blackford, the SNP’s leader in Westminster, issued an appeal for cross-party co-operation to prevent the “catastrophic damage” of an “extreme” Brexit.

Labour’s policy on Brexit is so ill-defined that Labour Remain voters are as convinced that the party is “completely against Brexit” as Labour Leave voters are convinced the party is “completely in favour of Brexit”, according to a YouGov survey.