Labour cannot win with Jeremy Corbyn as leader, Ed Balls has said – but adds that the party also “didn’t deserve” to return to power last year.

The former Shadow Chancellor has accused Corbyn of believing that the strength of support from his core sore supporters is indicative of the electorate at large, and of indulging in a “leftist utopian fantasy”.

Balls makes the criticisms in his forthcoming memoir, Speaking Out, which is being serialised in The Times. He is the latest major Labour figure to come out against Corbyn, and follows Ed Miliband endorsing challenger Owen Smith in the leadership contest.

In the latest revealing extract, Balls writes:

“Refusing to listen to the electorate has never been a winning formula, any more than Jeremy Corbyn thinking the volume of the cheering from your core supporters is a reliable guide to wider public opinion. Caution will not win the day; but nor will Jeremy Corbyn’s leftist utopian fantasy, devoid of connection to the reality of people’s lives.”

In today’s extract, he also writes about his difficult relationship with Miliband, and his frustration at forgotten passages about closing he deficit in the leader’s 2014 conference speech.

“The omissions were a symbol of Labour not being willing to face up to the problems the country was worried about, and proof that we were trying to brush difficult issues under the carpet. We weren’t ready — and didn’t deserve — to return to government. It was incredibly frustrating,” Balls writes.

“Having kept me at a distance in the run-up to the election in 2015, I think we probably only spoke twice in the whole four-week election campaign. That was astonishingly dysfunctional when I compare it to how Tony and Gordon worked.”