By Claire West

Brits using smartphones and tablets to catch up on work or on the news while commuting risk racking up extra charges that could collectively cost almost £685 million per year according to the latest research from uSwitch.com, the independent price comparison and switching service.

Seven in ten commuters (70%) are now using smartphones and/or tablets on their daily commutes for an average 22 minutes each way. That's two fifths (59%) of the average journey time of 37 minutes each way. It means that commuters clock up 900 minutes each month, and so are glued to their phones or tablets for almost 4 billion minutes each month between them.

But with just 5% of pay monthly deals currently offering unlimited data allowances, data-hungry commuters are vulnerable to hefty out-of-contract charges. More than four in ten commuters confess to having exceeded their monthly data allowances in the past, and more than a fifth (22%) go over their data limit at least every two months[4]. Commuters in the South West of England are most likely to exceed their data limits (63%) while Scots are most likely to exceed their limits every single month (14%). Those over the age of 55 are the most likely age group to incur out-of-contract data charges.

And it's easy to see how so many commuters are racking up extra charges. Just browsing the internet for 15 minutes, and sending or receiving ten emails with attachments, and ten emails without attachments, uses approximately 8.5MB of data, or 17MB per day, which works out at 342MB per month - and this is before mobile data used during the rest of the day is added.

Even a frustrating service isn't enough to make commuters put their phones down. They are undeterred from using their mobile internet connections in spite of the fact that more than half often get patchy connections (51%) and slow speeds (53%) on their journeys, while four in ten (40%) struggle with internet blackspots. Commuters in Wales report getting the most erratic connections (63%), but those in the East Midlands are most likely to suffer internet blackspots (48%) and sluggish download speeds (61%).

The top five mobile commuting activities are dealing with personal emails (65%), surfing the web (61%), using social media (47%), dealing with work emails (33%) and checking the weather forecast (31%). The most diligent commuters are in the South East of England as they are most likely to check their work emails on the way to and from work (42%). Those in the North West are the least likely to do this (24%), preferring to surf the web instead (65%).

Ernest Doku, telecoms expert at uSwitch.com, says: "Smartphones and tablets are both a blessing and a curse. They've quite literally changed our journeys to work, enabling us to tag an extra hour on to the working day, organise our social lives, catch up on last night's telly, or to simply zone out with an e-book or a news app. But as we get increasingly data-hungry, we need more generous data allowances at more competitive prices. And to make the most of our commute, we also need faster and more reliable mobile internet - the rollout of 4G can't come soon enough.

"Right now, only a very small proportion of pay monthly and SIM-only mobile deals come with unlimited data - just 5% - yet our research shows that 25% of commuters have opted for unlimited data plans. Unlimited data will likely make your mobile spend higher, but at least you won't get any nasty surprises at the end of the month. It can help consumers, and businesses that supply employees with mobile devices, budget better. So if you're going to be surfing the internet on-the-go with your mobile, make sure you've got the best package to suit your needs."

Top tips for avoiding extra data charges:

Use Wi-Fi where you can. Whether at home or at work, or via a hotspot when you're out and about, using Wi-Fi instead of 3G or 4G can help limiting your data usage and manage your bills. But if you don't have unlimited downloads at home, keep an eye on your usage there too.Keep an eye on your usage.

Track how much data you're using throughout the month through your online account. Some providers will also notify you when you're nearing your data limit.

Consider a data bundle. If you use up your allowance, talk to your network about what data bundles you can buy to see you through the rest of the month.

Upgrade your package. If you keep going over your data allowance consider a new deal - with more, or even unlimited data. If you like your phone, consider a SIM only deal that gives you more data.