Sam Billings laughs lots, smiles more, and has a growing reputation as gregarious company in cricket teams the world over. It's easy enough to see why; Billings is a decent mimic (particularly of Danny Morrison), has quirky catchphrases, relishes his mates' success, and much of that laughter comes at his own expense. He also has that happy knack of making the game - all rubber-wristed batting, athletic keeping and dizzying fielding - and the itinerant world of the Very Modern Cricketer, a genre of which he is the archetype, look enviably fun.

Yet, despite the notably cheery disposition, and despite being lumped with the pet name handed to English cricket's dabblers and dilettantes, Jazzer, the blue-eyed boy has a serious, sterner side.

As evidence, take England's tour of Bangladesh in October, where Billings went unselected for the first two ODIs, despite the absence of Alex Hales, Joe Root and Eoin Morgan. Given the unavoidable security measures, this was a strange, claustrophobic tour with few hiding places, and a familiar sight emerged: Billings, in the gym with England's fitness staff, hammering himself.

A day out from the decider, his old mate and now captain Jos Buttler came to tell him he would open the batting - a significant promotion (he had never batted higher than No. 6 for England). "I was a bundle of energy that day," Billings said. "I think the GPS showed I did 18km in the field, which is mad in that heat. I was chewing it over, thinking that everyone expects me - the way I play, as a finisher, a T20 slogger, 'only shot he's got's the sweep' - to get 20, maybe 30, off 20 balls. I just wanted to show people I was capable of doing well out of my comfort zone."

Chasing 278 for a series win, Billings made a measured 62 with some trademark sweeps, but plenty more classical strokes, before falling at the halfway stage. Thankfully, England got home, leaving him relieved but unsatisfied. "I should have been there at the end with 120," he says.

"In age-group sides, I couldn't get it off the square, I was too small. But not being good enough spurred me on, because - as clichéd as it sounds - I hadn't ever wanted anything other than to be a sportsman"

This innings is one of a number of impressive knocks he recalls with uncompromising clarity in which he was simply "trying too hard". His first innings for Sydney Sixers, 42 against Hobart Hurricanes (the top score), is another. "My girlfriend's learnt how to deal with me coming home and being hyper-critical," he laughs.

Last year was a breakout one for Billings. In terms of global leagues, his was the most nomadic year of any current England player, ever. Away from his white-ball international commitments in South Africa, at the World T20, during the home summer, and in Bangladesh, Billings played for Islamabad United in the PSL and Delhi Daredevils in the IPL. He then went back to Kent to play all three formats, with a bit of England Lions thrown in, before ending the year at the Big Bash with Sixers. He only opted out of the Bangladesh Premier League to briefly catch his breath.

That he was drafted by Islamabad - who won the PSL - was something of a surprise, but also the catalyst for much that followed. They chose him due to the 24-ball 50 he made against Pakistan in November 2015, a decision supplemented by his stats for Kent. He was green, say staff, but also the overseas player most willing to mix with locals and embrace every aspect of the experience; it is little surprise that, as with Delhi, he was retained by Islamabad. PSL colleague Brad Haddin pressed his case when Sixers sought a second overseas player to join Billings' close friend Jason Roy. In Sydney, team-mates talk glowingly about his impact, and opposition have scratched heads as to why Billings batted down the order.

"I had the time of my life in 2016," he says. "It's been amazing. I've probably made 100 new mates across the world, and I absolutely love that. That's what's special about the game. I've played at grounds I've dreamed of playing at, and in front of huge crowds. The pressure of being the overseas player is huge. I've learned a huge amount, rubbed shoulders with some of the biggest names in the sport, and I've improved hugely as a cricketer. The IPL was a bit of a blur, but in the BBL, at Adelaide Oval on New Year's Eve, there was a moment I just took it all in. Looking up at the huge new stands, I just thought, 'How good is this? A world away from a freezing cold farm in Kent!'"

There is a but. Of course there is with someone so demanding of himself. "On the flip side, that one in Bangladesh was the first ODI I'd played in over a year, and I only played a couple of T20s this year, despite being in lots of squads. I have so much to improve on." Billings, it seems, is too enterprising to settle for life as a gopher, waiter and cheerleader, so his overall response to last year is the same as it was in Bangladesh: get fitter, work harder, be better. If there's a conversation to be had about the game, or a means of bettering his, "I'm always going to throw myself at it."

T20 leagues are part of this: a life experience, not - as they are for some - a quick buck. "If I wanted to earn money, I wouldn't be playing cricket," he laughs, "I'd be working in the city!" This explains why he entered the IPL auction at the low base price of £30,000 - approximately one-eighth of Ben Stokes' price this year - and enough to make an overall loss, due to the fees English players have to pay their counties (about 1% of their salary for each day missed) when spending time away.

Because Andrew Strauss encouraged Billings to enter the auction and he does not have an England contract, the ECB felt obliged to reimburse him, although the enthusiasm with which he speaks about the experience suggests he would happily have played for free. He relished working with and under the likes of Zaheer Khan and Rahul Dravid, and he is not the only current cricketer to vividly recall chatting with Virat Kohli. "He told me he believes he has 15 years to improve our sport. That struck a chord."

And then there was what Kohli said about fitness, which shaped Billings' spell in Bangladesh but also linked back to his degree at Loughborough University. "For me, fitness has got to be a non-negotiable in the modern game," he says. "It's a real base issue of where you are mentally. The sports science I did at uni taught me that fitness and psychology go hand in hand - if you are pushed to your optimum, you become more emotional and more raw character shows. That's the purpose of preparing better - to get fitter, so my ceiling is higher and I'm calmer and I can perform better in those high-pressure situations. Kohli said he wants to be the fittest cricketer on the planet, and if it's good enough for him…"

Billings only went to Loughborough because he was not yet good enough at cricket. "Honestly," he says, "I was crap at school. Nowhere near good enough to go from the Kent academy, where I'd been for a few years, onto the staff and get a contract. Growing up, coming through the age groups, blokes like Jos, they were miles ahead. In England age-group sides, I played as a keeper and lower-order batsman. I couldn't get it off the square, I was too small. But not being good enough spurred me on, because - as clichéd as it sounds - I hadn't ever wanted anything other than to be a sportsman."

Billings is brutally self-critical and brazenly ambitious, while oozing talent and at once being silly and serious. All that might just make him England's most interesting cricketer

University helped him "learn to look after" himself, and appreciate "how important self-discipline would be", but also - through the MCCU scheme - handed him a first-class debut, in 2011, during which he scored a century against Northamptonshire; since then, the upward curve has been continuous, culminating in his stellar 2016. It's hard to avoid the conclusion that his appetite for graft means this is not a coincidence. He was inspired by reading Matthew Syed's Bounce: talent is one thing, but the best, he believes, work hardest.

His aims for 2017 are clear. Among England players, he's not alone in being profoundly moved by James Taylor's story, and is thus determined to continue enjoying every minute. He wants to be impossible for England to ignore in white-ball cricket, and eventually wants to play Tests.

But for all his extra-curricular activities, he also wants to pull Kent forward; it was hard to question his commitment to his county when, in September, he drove through the night from Manchester to Beckenham in the ultimately futile hope of salvaging a Championship draw against Northants, having been England's 12th man against Pakistan the previous evening. He has offered to assist in wooing overseas signings and wants to set an example. On returning to pre-season training in November, he - unsurprisingly - topped fitness testing, but was shocked to see senior pros not only lagging behind but cutting corners too. That disappointment was not hidden.

Billings says what he thinks, and is not afraid to seek new peaks. He is brutally self-critical and brazenly ambitious, while oozing talent and at once being silly and serious. He has plenty of competition, but all that might just make him England's most interesting cricketer.

Will Macpherson writes on cricket for the Guardian, ESPNcricinfo and All Out Cricket. @willis_macp