Yvette Cooper treated herself to a morning off from the campaign trail last weekend. It didn’t sound very relaxing, though: she and Ed Balls, her husband, went for a dip in the chilly waters of the North Sea at Sheringham Beach. A strange fondness for cold, sharp shocks is certainly an advantage in the senior ranks of the Labour party, for whom the pain of defeat has been compounded by the spectacle of seeing tens of thousands of new supporters paying £3 to vote for the left-wing radical Jeremy Corbyn.

Ms Cooper’s pitch to her party is simple: she is the only woman who can stop him. Corbyn now dominates the race. At hustings and interviews, the candidates are asked as much about their Jeremy Corbyn policies as they are about welfare, fracking and spending cuts. Cooper has been preparing for this contest for years, whereas until a few months ago, Corbyn had been planning to spend this summer on his allotment. Now bookmakers put his chances of winning at 85 per cent — and Yvette Cooper’s at 9 per cent.

She still seems rather cheery when we meet. She says there was a ‘hard’ first month when Labour mourned the loss of another election. ‘Now the party’s already got energy back, so it’s really fun going round, doing events and things.’

The energy, of course, has largely come from 66-year-old Corbyn. All of the other candidates are now defined by their thoughts on him, and Cooper has hers ready. ‘The things I strongly disagree with Jeremy on are about printing money, and also I think probably the internationalism as well, membership of the EU and membership of Nato.’

Would Jeremy Corbyn as a Labour prime minister damage Britain? This is an awkward question for the Labour MPs who may soon be paid to campaign for his entering No. 10. ‘I think some of [his policies] will be damaging, but some of them I think are just backward-looking when I think we should be forward-looking,’ she says. ‘In the end, because they wouldn’t be credible, they will also make it much harder for Labour to win the next election. Then we’d be letting so many people down.’ As support for Corbyn has grown, so have Cooper’s warnings about the danger of voting for him.

This week she also accused ministers of being ‘cowardly’ and ‘immoral’ over the refugee crisis, and suggested Britain should take 10,000 asylum seekers from the Middle East. She claims that her ‘controversial’ argument counters accusations that she is cautious and boring.

Perhaps this new, bolder tone is keeping her cheerful. Whatever the reason, she chuckles often, lolling on a sofa. It’s a glimpse of the Yvette Cooper which her friends promise exists: a cheerful soul with a naughty sense of humour that gets buttoned into the perfect politician every time a camera or microphone comes anywhere near.

She has a jovial poke at Charles Moore, who observed in his Spectator’s Notes recently that a candidate’s looks matter in leadership elections — and that Cooper has ‘something quite appealing about her slightly French crop and black and white dresses, especially when she is so boring that one looks rather than listens’. His remarks created a minor storm on Twitter. Nicola Sturgeon, the SNP leader, and Ruth Davidson, the leader of the Scottish Conservatives, led protests. It was ‘the most hilarious old-buffer politics’, she says, collapsing into giggles. ‘The most absurd and outrageous thing. I wasn’t sure whether he said that I might — I just might! — have the looks. It’s like: thanks Charles! I couldn’t quite work out if his argument was because he thought Tory backbenchers would fancy me like they had Margaret Thatcher. You know, that’s one demographic I’m really not appealing to.’

Cooper herself has come in for plenty of criticism on Twitter during this campaign. She says she reads it ‘sporadically’ on her archaic BlackBerry, but she’s aware of being called a ‘Red Tory’ — the implication being that she’s a traitor to Labour. What is happening to her party? ‘I think there’s a sense of frustration and anger and wanting change,’ she says. ‘We shouldn’t underestimate the impact that a five-year parliament has on the party — the next election feels a long way away. I guess my message to the party is that we’ve got to make sure that change is about changing the country — not just about changing the party.’

It’s not always clear what drives Cooper, so I ask. She talks about her upbringing in Hampshire as the daughter of a trade unionist from a coalfield community: ‘It was always that feeling that if you’ve got a neighbour that needs help, you should, if there’s something you can do to make things better or to change things.’ She says she ‘tumbled into becoming an MP because I was always involved in campaigns’ and was ‘slightly taken by surprise that I was then selected in 1997’.

Cooper didn’t seem especially surprised when Labour lost this year’s election. The party’s offer was ‘too narrow’ (a convenient phase which avoids questions about moving left or right). Labour failed to win the suburbs, towns and particularly coastal towns, she says, because the Tories made a better ‘pitch to security and to fear’. She tells of meeting a business-woman at the CBI dinner after the election who said: ‘You broke my heart at the election because I felt like you didn’t want my vote.’

She has refused to apologise for Labour’s economic record, and her new economic pitch is upbeat and intertwined with agree-able talk about high-tech jobs. She is also very keen on ‘changing the way the economy and actually also public services work, and putting family at the heart of it… what I don’t think we did over the last five years in opposition was talk about family’.

She says she’d defy Corbyn on ‘something like Europe’, but ‘It’s not going to be my style to vote against the Labour whip 500 times like Jeremy!’ Her eyes widen at the thought of serial bad behaviour. Even in this relaxed mood, it’s not really something Yvette Cooper can even imagine.