Ed Balls, staple of Britain's Labour party and former Shadow Chancellor of the Exchequer, told CNBC on Wednesday that his party is in the process of a "big change," albeit not one he expected or supported.
However, "what I'm not going to do is prejudge Jeremy Corbyn at this stage – he's the leader, he got elected, it's quite a big experiment and the proof of the pudding will be in the eating," Balls, who was speaking to CNBC at the Institute of International Finance conference in Madrid, said.
"There's clearly issues around economic security but also aspiration, also the security of our nation – those are big questions and the Labour party's got to debate those things and set out its policies and some of them are still quite disputed," Balls told CNBC.
Corbyn, who was seen as a surprise choice for Labour leader when he was elected in 2015, is known to be more left-wing than previous party leaders. His views include an opposition to nuclear weapons and a strong focus on workers' rights.
Although the party has clearly moved on from Tony Blair's New Labour program of the late 1990s, said Balls, the fundamental belief of being credible and showing that the "sums add up in order to at the same time show you could change your economy and your society to make it stronger and fairer," still stand in today's Labour party.
"It's a different time, populations are angry when they look at what's happened around companies not paying their tax while their income stagnates and that's something we have to rise and respond to which is different from 10 - 15 years ago but that fundamental insight – to be radical, you have got to be credible, that's not changed."
Balls also addressed the recent controversy around anti-Semitic remarks made by some members of the Labour Party leaders, telling CNBC that the anti-Semitism in the party is "disgraceful and the leadership is, I know and I absolutely hope, cracking down on that."
Balls, who has been campaigning with Conservative party member and Chancellor Exchequer George Osborne against Brexit – the vote on whether Britain will stay or leave the European Union – acknowledged it was surprising that he was working alongside his great political rival.
"There are some things which are bigger than party politics. We're making decisions which will shape Britain's future for the coming decades," he told CNBC.
"On Europe, George Osborne and I totally agreed joining the single currency would be bad for Britain and on this EU issue and the referendum, we both say we should stay in and fight our corner," said Balls.
"I think it was a good signal to send out to the public – people who can have deep disputes, about values, about policies, tax credits or the pace of deficit reduction, when it comes to this big question of Europe - we can agree, and the signal to people out there is if you are undecided, whether you are blue or red, if you care about the future of our country, you should vote in."
The referendum vote is set for June 23, with the latest polls indicating that the majority of British voters do not want to leave the EU.