Labour's Dan Jarvis meets me at Barnsley station and gives me a brief tour of the town before we settle in a local café for lunch.

He's suited, short back and sides, polite, and incredibly enthusiastic about his constituency. He tells me that whenever he walks into the House of Commons he reminds himself that he's there to speak up for his constituents.

"I'm a doer I like to get things done and there's so much to do," he says.

He wasn't widely known beyond Westminster until he shot to fame after last May's general election.

Labour lost; Ed Miliband resigned; and he found himself the hot favourite to win a leadership contest. Over a couple of days he was pursued by "Dan fans" and dogged by reporters and film crews as he considered whether or not he should stand.

Listen to Becky's interview with Dan Jarvis on BBC Radio 4's PM

'Appalling times'

Why you? I ask him. To his credit he doesn't take offence.

"I don't know. I mean there had been a bit of gossip and speculation before the election… some people were quite forceful in the way that they suggested I put myself forward."

But in the end he decided against standing, saying "it wasn't the right thing for my family at that moment".

His two eldest children lost their mother, his first wife Caroline, to cancer in 2010.

He tells me: "These are just the most unspeakable, appalling times when you have young kids you don't have the luxury of going into yourself, because you've got to keep the show on the road.

"For myself, if I'm being sort of brutally honest about it, I think that I'm probably at my best when my back is against the wall, when you kind of suffer a bereavement you suffer that kind of tragedy, there's a huge pressure that comes from it, and you can either sink or you can swim… and I decided to start swimming."

He left the army - he was a major in the Parachute Regiment - and stood for Labour in the Barnsley Central by-election, and won.

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He has revisited his decision not to go for the Labour leadership in a recent interview for the Guardian newspaper.

"I'm not a great one for regretting anything, but what I do regret is that I didn't give it more thought beforehand," he says.

More recently, speculation revved up again about his leadership ambitions and he was accused of being disloyal.

He rejected the criticism, telling me that he has never and will never criticise Jeremy Corbyn.

"It's not my style", he says.

I ask him about his leadership ambitions. "I don't lie awake at night thinking about it, I think what I've come to know is you never know what's around the corner, and you have to be ready for anything.

"My focus is getting on with job as the MP for Barnsley Central."

He adds: "If people say you bottled it, it doesn't affect you. Well it doesn't affect me, because it's just nonsense."

Full English

We order our lunch, he has a full English Breakfast, he won't need to eat again today, I say.

He grins. "I probably will though".

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He's wary of talking about his military career, he doesn't want it to define him and worries he might be accused of showing off.

He served in Kosovo, Sierra Leone, Iraq and Afghanistan and lodged in his skull is a small fragment of shrapnel.

Rather than the military adventures - which I am fascinated by - what he wants to talk about is his vision for the Labour Party and how they can win the next election.

He says the party has a mountain to climb, but he's optimistic. It comes down to two very simple things, he says: "You've got to have credible people and credible policies and ideas."

'Jeremy's a decent guy'

I ask if Mr Corbyn and shadow chancellor John McDonnell are the credible people he is talking about.

"In the end it doesn't matter what I think, because it's for the public to decide."

So, does he believe the public thinks they are credible?

"Look, I think that Jeremy is a really decent guy, many of the things that Jeremy talks about resonate with millions of people, the challenge for him and for all is, basically, now, to take it out to the country, because our membership is incredibly important.

"But it represents just a slither of the population and in the end we've got to convince the public that we are credible - and if we don't we will lose again."

Image copyright PA Image caption Former Labour leader Ed Miliband celebrates the victory of Dan Jarvis in the Barnsley Central by-election, in 2011

I order us more tea and I ask Dan straight: Is Jeremy Corbyn a future prime minister?

"I hope so," he says.

We have a chat about his near death experience on Snowden, being stranded in remote Nepal, with his military mate David, who is now an international male model, and how he refused to hand over his wallet to a mugger.

He glances at his watch and can't believe the time: "My office will be fainting because they've lost track of me for about three weeks."

One last question.

His best mate Dave, living the high life as an international male model. Fast cars, fancy do's.

Does he ever think he pulled the short straw? Oh no, he is the lucky one, he answers, the one who is privileged and honoured.

When he falls silent, I tell him I think it sounds quite exciting.

And after a pause - and it might be the first time he really lets down his guard - he laughs. "Yeah it does, doesn't it?"