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Jeremy Corbyn suffered a blow today as a new poll showed his rival Owen Smith soaring into a commanding lead on which of them would make the best Labour leader and Prime Minister.

The survey for the Standard found that 57 per cent of the public favoured Mr Smith as party chief, against 43 per cent for Mr Corbyn.

On the question of who would make the best premier, the findings by BMG Research were exactly the same.

More than half of adults — 57 per cent — also believe that Labour under Mr Corbyn is failing to provide a proper opposition to hold the Government to account, with just 16 per cent saying it is.

But the findings are in stark contrast to those for Labour supporters, suggesting Mr Smith has a huge task to win over enough party followers to become leader in September.

Three quarters of people intending to vote Labour at the 2020 general election say Islington North MP Mr Corbyn would make the best party leader — and PM — while just a quarter name Pontypridd MP Mr Smith.

This is despite 44 per cent of Labour backers believing that the party is failing to provide a proper opposition to the Tories, compared with 38 per cent who think it is doing so.

Michael Turner of BMG Research said: “All the evidence suggests that Labour would be far more electable under Mr Smith.

“People who currently would not vote for the party but say they may consider it are far more in favour of a party led by him.

“He is also more attractive to current Liberal Democrat and Ukip supporters. But Mr Corbyn is still hugely more pop- ular among current Labour backers.”

Mr Turner also described Labour as being in a “bizarre state of cognitive dissonance”, given the strong support for Mr Corbyn despite the recognition that the party is failing to challenge the Government.

Dozens of MPs have resigned from Mr Corbyn’s shadow ministerial team, urging him to stand down.

Mr Smith was little known outside of Westminster until a few weeks ago but his combative style has shot him into the media spotlight, with strong attacks on Mr Corbyn — though some comments have backfired. He was forced to apologise yesterday after suggesting Labour should “smash” Prime Minister Theresa May “back on her heels”.

In his bid to be leader, he proposes a new wealth tax, bringing back the 50p top rate of income tax, reversing cuts to inheritance tax, more NHS spending, an end to the public sector pay freeze and outlawing zero-hours contracts.

Mr Corbyn has pledge new policies to deal with inequality and austerity.

The poll also showed that if he is still leader in 2020, nearly a third of adults would be either less likely or far less likely to vote Labour, compared with 21 per cent for former shadow work and pensions secretary Mr Smith.

But 52 per cent of Labour supporters said they were more likely or far more likely to vote for the party with Mr Corbyn at the helm — far more than the 28 per cent for his challenger.

More than a third of the public believe Mr Corbyn is putting his own interests first by clinging on as Labour leader despite a motion of no confidence in him by party MPs. Among Labour supporters the figure is just 19 per cent.

BMG Research interviewed 1,551 UK adults online between July 22 and 26. Data are weighted.