Senior Labour MPs have accused their party leadership of paving the way for a hard Brexit while aping the populist language of Nigel Farage.

Shadow Chancellor John McDonnell is facing a furious backlash over a speech, which urged Labour to “embrace the enormous opportunities” of withdrawal – instead of fighting to prevent its most damaging consequences. Mr McDonnell also horrified many high-profile backbenchers by accusing pro-Europe MPs of siding with “corporate elites” – a charge normally levelled by Ukip.

The most incendiary sections of the speech were briefed in advance to a right-wing newspaper only, adding to suspicions that the Labour Chancellor is attempting to bounce Labour into a tougher anti-Brexit stance.

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A string of former shadow ministers told The Independent that the shift would make it easier for the government to pursue the hard Brexit apparently sought by Theresa May.

Yet Labour, in alliance with up to 30 Tory MPs and the other parties, has a potential Commons majority in favour of staying as close as possible to the single market, to protect trade and jobs – a so-called soft Brexit.

One prominent Labour MP said: “John gives the impression that we will simply lay down and accept a hard Brexit with joy in our hearts, but that is a million miles away from where the Labour Party should be.”

A second warned: “If we carry on with that sort of language, it will play into the hands of the hard Brexiteers, who claim we can leave the EU without the downsides and the risks.”

And a third, a former minister, turned on Mr McDonnell for suggesting anyone making a pro-Europe case was somehow playing the game of “corporate elites”. “A lot of people see the EU as having done much to preserve peace, to introduce good employment and environmental standards and having allowed Britain to be a good place to invest,” he added. “They don’t want to be told that, if they believe those things, they are in the pocket of corporate elites – which is the Ukip, nationalist, right-wing position.”

During the speech, delivered the week before last, the shadow Chancellor raised eyebrows by saying: “We must embrace the enormous opportunities to reshape our country that Brexit has opened for us.

“This means we must not try to re-fight the referendum, or push for a second vote and, if Article 50 needs to be triggered in Parliament, Labour will not seek to block or delay it. To do so would put us against the majority will of the British people and on the side of certain corporate elites, who have always had the British people at the back of the queue. It is time we all were more positive about Brexit.”

The Labour MPs criticising Mr McDonnell insist they accept the referendum result – but not that their party should give the Prime Minister a free hand to end free movement of people at whatever cost.

Most spoke off the record, to avoid re-starting internal party wars, but said they will continue to oppose the policy shift.

One, former shadow Chancellor Chris Leslie, did speak openly, saying: “Labour has got to intervene in this process, to protect the economy and public services from the hard landing likely as we fall out of the European Union.”

A second, former local government spokeswoman Emma Reynolds, has written an article highlighting the danger of Labour learning the wrong lessons from the Brexit and Trump successes. Ms Reynolds condemned the “simplistic solutions offered by right-wing populists, who have successfully constructed a powerful narrative that we are a self-serving and out-of-touch elite”.