A senior pro-EU Labour MP has claimed leaked emails between Jeremy Corbyn and a senior ally showed “in technicolour” that Labour’s EU referendum campaign had descended into confusion.

Former frontbencher Chuka Umunna said the messages in which Labour election boss John Trickett asked his leader’s permission to “amplify” criticism of the EU, demonstrated Labour’s pro-Europe stance was not whole-hearted.

Mr Umunna dismissed as “nonsense” Mr Trickett’s claims in one email that the party’s line was being pressured by “loads of Labour Euro-fanatics”.

Speaking after the emails emerged, the former shadow Business Secretary said he was now more disappointed an enthusiastic effort to stay in the EU was not made.

He said: “This illustrates in technicolour why there was the confusion.

“What it all helped contribute to doing, was handing the populist right and the nasty divisive politics of Nigel Farage, the biggest victory they have ever seen in this country.”

The emails written in February and later leaked to the Guardian, contained two documents setting out how the party might respond to the Government.

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Hemsworth MP and shadow Business Secretary Mr Trickett wrote: “I would like permission to amplify the critical, pro-reform part of the agenda on the basis that I accept that I can’t follow my instinct to vote and campaign for ‘No’.

“There will be loads of Labour Euro-fanatics pressing an uncritical case; so at least one of us needs to speak to the hundreds of thousands of Labour voters who are (correctly) sceptical of the EU.”

Mr Trickett later said he had no formal role in the campaign, and that while he was wary of supporting the Remain camp when he sent the email, he was then personally persuaded to back the party’s official pro-EU stance by Mr Corbyn.

Streatham MP Mr Umunna said: “The idea that there are a bunch of Labour ‘Euro-fanatics’ is nonsense.

“All of those who argued strongly for us to stay in the EU recognised that it needed reform and said so.