Shadow chancellor says he is worried another referendum would embolden the far right

John McDonnell has backed a Labour colleague who warned that a second Brexit referendum could lead to social unrest.

The shadow chancellor told BBC Radio 4’s Today programme he agreed with Barry Gardiner, the shadow international trade secretary, that anything seen as an attempt to undo the result of the EU referendum could embolden the far right.

But despite those reservations, McDonnell insisted that the Labour party was not ruling out a second referendum and that another vote remained an option if parliament was deadlocked in the autumn.

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On Tuesday Gardiner delivered a grave warning about the social disruption a second referendum might cause, in terms that implied he considered the idea completely unacceptable.

Two days later his position was dismissed by Sir Keir Starmer, the shadow Brexit secretary, who said a second referendum was an option for Labour and gently mocked Gardiner’s predictions.

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“We’ve had lots of ups and downs already on Brexit ... and I have not seen signs of civil disobedience. So I think we can get through this exercise without that,” Starmer said.

Asked to adjudicate between his colleagues on Friday, McDonnell said: “We have to be extremely careful. A number of us now are worried about the rise of the far right in this country, and elsewhere, and what we mustn’t do is open up any opportunities to the far right exploiting this issue.

“We have already seen violence on the streets from the far right, when we saw the Tommy Robinson demonstrations and the attacks on the police and others. So Barry is right to caution about how we handle this issue.”

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But McDonnell did side with Starmer about a second referendum being an option for Labour, although not something the party was actively proposing.

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“It is not Labour party policy to have another referendum. We respect the past referendum,” McDonnell said.

“But we recognise that, when the government comes forward with its proposals – if it does, I’m worried we might be in a no deal situation – but when the government comes forward with its proposals, parliament will decide the next step. So we’re not taking any options off the table when that debate happens.”