Len McCluskey, general secretary of the Unite union, told Politico it would be a success for Labour if it could hold onto 200 seats in the 650-seat House of Commons - or 29 fewer than the party now holds. People like me are always optimistic. things can happen. I'm full optimism for what Labour can achieve. "I think it would be extraordinary".
"It will mean that Theresa May will have had an election, will have increased her majority but not dramatically".
Labour's spending plans would open up a £58 billion "black hole" in the public finances, the Conservatives have warned. Angela Rayner, who despite leading a strident campaign against Tory plans for more grammar schools, has supported colleagues who want to send their children to one; Emily Thornberry, who opposed selling off council houses, but bought one to rent out.
When Parliament was dissolved at the end of April, Labour held 229 seats compared to the Tories' 330.
However, the poll of polls - the average of many polls that are carried out - put the Tories on 47 and Labour on 31.
"The reality, of course, is that Labour has launched their manifesto, a fantastic manifesto, a manifesto for workers, for ordinary working people and a manifesto which will change Britain for the better".
The latest opinion polls have Labour around 30% or more with the Conservatives above 40%.
If Labour were to win 200 seats, that would represent its worst result since 1935.
A Conservative spokesman said: "Jeremy Corbyn can't deliver any of this - it just doesn't add up".
On the chances of a Labour victory, Mr McCluskey said: "In terms of the imagery of Jeremy, that's a huge task".
The actor, producer and director - who shot to fame with his role in TV's Taxi and classic drama One Flew Over the Cuckoo's Nest - said the United Kingdom has "got the guy". And I just say this too - this could be a young person's election, because large numbers of young people are registering, for the first time those interested in politics want to have their say.
On who would make a better prime minister, juts over half - 56 per cent - of respondents favour May, with 29 per cent backing Corbyn.
Scottish Labour believes that together we're stronger.
In the run-up to last year's USA election, the actor, who has had a career spanning more than four decades in Hollywood, urged people not to vote for Donald Trump. "There is everything to play for now and we'll be fighting for every single vote".
Mr McCluskey claimed he was not setting a benchmark on which his own support for Mr Corbyn rested.