Nick Clegg might suffer from a reputation for struggling to keep promises, but he claims to have made a breakthrough on one long-running ambition: to give up smoking.

The Deputy Prime Minister has become a convert to ‘vaping’, in particular using a blueberry flavoured e-cigarette which helps him unwind at home in the evenings, with the occasional glass of Spanish white wine.

In the most revealing moments of his interview with MailOnline, he discussed how he has learned the hard way not to speak for his wife Miriam, made unconvincing claim to enjoy spending every summer holidaying in the Spanish village where she grew up and explained his battle to keep his children out of the public eye.

He also discussed his worst habits, his wealth and the disgusting chocolate and Twiglets combination he enjoyed as a child.

Deputy Prime Minister Nick Clegg has become a convert to ‘vaping’, in particular using a blueberry flavoured e-cigarette which helps him unwind at home in the evenings

No matter what his opponents, commentators and the polls keep telling him, the Lib Dem leader remains in a defiantly upbeat mood.

As Deputy Prime Minister for the last five years he has toured the world, met the great and the good and been at the heart of an extraordinary experiment in coalition government.

But the thing he is most pleased to have done is feed a seal in Cornwall.

’It was brilliant,’ he says with schoolboyish enthusiasm. He sent a picture of his moment with the seal to his children, his parents, his whole family.

His baffled sister asked: ’Why is this the only picture you've emailed me of yourself in the last several months”.

I recommend the blueberry vape. That’s quite different to the Marlboro Lights

But he insists: ’I was so excited about that.’

It is unusual to find such an upbeat outlook in someone trying to quit smoking, but he insists - not for the first time - that he might just have managed to kick the habit.

In 2011 Mr Clegg revealed he had gone ‘cold turkey’ to give up smoking, but it did not work.

Two years later he declared he was ‘off the ciggies’, but admitted it might not last. It didn’t.

But now there may have been a breakthrough. ‘It has taken a significant step in the right direction,’ he declared.

‘At the moment, at least for the last several weeks, I am off the fags and on the vapes. I’ve got some hilariously termed multi-voltage thing.

‘I haven’t smoked a cigarette in weeks. I’m not 100 per cent sure what the effect on my health is of these new battery powered things,’ he laughs.

‘You can put all different flavours in it. I have tried the blueberry, it’s good. I recommend the blueberry vape. That’s quite different to the Marlboro Lights.'

As Deputy Prime Minister for the last five years he has toured the world, met the great and the good and been at the heart of an extraordinary experiment in coalition government but the thing he is most pleased to have done is feed a seal in Cornwall this week

Reclining on a large cream sofa in his office over-looking Horse Guard’s Parade, he claims never to have used his e-cigarette at work, but it does mean he is no longer banished to the garden when he needs a nicotine fix at home.

‘I now don’t need to cower in the rain. I only ever smoke very little, only in the evenings when the kids have gone to bed and all the rest of it.

I’ve learned the hard way not to speak for Miriam. She’s not shy in coming forward with her view

‘It’s just a great opportunity to turn the phone off and have a bit of time to myself, but now I can do that indoors as well as outdoors which is another hidden advantage.’

Mindful of his reputation for broken promises, he is not yet ready to say that he has kicked the habit for good: ‘I’m not going to over claim and under deliver on this particular instance. That is the current state of affairs, it is a changeable situation or could be.’

In a week when Ed Miliband turned to his wife Justine to bolster his flagging poll ratings, there is growing expectation that Miriam will step out in support of Mr Clegg.

She may well hit the campaign trail at some point. He is just waiting to be told.

‘I’ve learned the hard way not to speak for Miriam,’ he says, with a cautious laugh. ‘She will speak for herself.

‘But Miriam… she’s not shy in coming forward with her view from time to time and that’s one of the many, many, many things I love about her.’

Mr Clegg said he hopes wife Miriam will join him on the campaign trail at some point. He is just waiting to be told

As Labour gears up to deploy Mrs Miliband as the Labour leader’s secret weapon, Mr Clegg hopes his wife ‘will hopefully help out a bit’ in the election campaign, while juggling the pressures of her job as a City lawyer and raising their three sons Alberto, Antonio and Miguel.

‘One thing I can tell you, both Miriam and I will always be vigilant about trying to keep the kids out of the public eye, he says.

He insists it is not meant as an ’oblique criticism’ of the Milibands, who had their sons Sam and Daniel pose for the cameras this week.

‘But we have been very adamant right from the outset that we are not going to have our children… I will talk with unbridled pride about my children, and very happily do that like any proud dad.

‘But I just don’t want them in the public eye.’

It is difficult to get further from the public eye than the small town of Olmedo where every year the Cleggs take their summer holiday, with Miriam’s family.

Mr Clegg insisted he really does love going to the small town of Olmedo, Spain every year

Surely he must tire of the same break in the middle of nowhere? ‘You have no idea what a dangerous question this is. Upon this answer hinges my long-term fate.’

Nervous laughter. ‘I absolutely love it. I love um… I love… no I really do. Where my in-laws live really is kind of in the middle of nowhere.

‘I’ve been going there for over 20 years or so now. It’s completely off the tourist trail. I don’t think I have ever seen a tourist there.’

But is it fun? ‘Well it is… I love it because it’s… I love it because… it’s a complete change of gear. The kids play football with the other kids in the village and I play tennis my brother-in-law with some folk who live in the village.

‘It’s village life in the middle of nowhere and it’s just a wonderful way of getting away from stuff.’

That ‘stuff’ includes the ongoing speculation about his own political future.

MailOnline readers were blunt. Atavist, Little Oakley: ‘When the removal men drop your stuff off in Spain in June, will you be renting your house in Sheffield to students?’

Jane, SouthWestCountry: ‘Will you rule out a job in Brussels when you lose your Sheffield Hallam seat in May?’

Sandy Brown, London: 'Mr Clegg. When you leave office in May where will you go. Will you get another job say working in Tesco?'

But he laughs it all off: ‘I genuinely, genuinely think, much as there is this great cottage industry of pessimism from the pundits and my critics, I think we are going to do some much better than people say.

‘Of course I hope, and am confident but not complacent that I will continue to service the people of Sheffield Hallam as an MP. That’s exactly what I intend to carry on doing.’

And has the former MEP given any thought to a return to Brussels? ‘Oh God no.’