The former Prime Minister Gordon Brown has weighed in on the Labour leadership battle for the first time following Tony Blair's warning against electing Jeremy Corbyn.
Brown said the party must be credible and electable and can only deliver its principles in power, while speaking on "power for purpose" at an event at the South Bank Centre on Sunday.
"Leaders come and leaders go. I know that. Politicians are here today and gone tomorrow," he said.
"We can only measure the progress we make by the difference we make in people's lives. It is not an abandonment of principles to seek power and to use that power in government. It is the realisation of principles."
Brown said he was "not here to attack any individual candidate". However, he distanced himself from Corbyn, saying the party could not "just return to the policies of the past".
A spokesperson for Corbyn's campaign responding to Brown's speech, said: "Gordon Brown has highlighted the need for a Labour party that stands for hope: that is credible, radical and electable - on which basis the best candidate to vote for is Jeremy Corbyn."
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It comes as a new poll revealed the extent of Corbyn's polarising image among voters, being named the candidate who is both most likely to worsen and improve Labour's chances of winning the next election in a ComRes survey for the Sunday Mirror and Independent on Sunday.
The poll found 21 per cent of people thought Corbyn would improve the party's current chances of winning the next General Election, while 19 per cent said the same of Andy Burnham, 15 per cent of Yvette Cooper and 11 per cent of Liz Kendall.
Meanwhile, 31 per cent Corbyn would worsen Labour's chances, compared to 14 per cent who said the same of Burnham, 18 per cent of Cooper and 17 per cent of Kendall.
An overall net score from the polling, which also includes those who said they didn't know who the person was or were unsure, puts Burnham ahead as the only candidate to improve the party's chances and leaving Corbyn as the most likely to worsen them.