We spent a day traipsing around London with Broadband Genie to find out whether public Wi-Fi hotspots offer sufficient coverage that you don't need a cellular connection. How good is public Wi-Fi? Read on to find out. (Visit Broadband Advisor for more.)

It started with a claim. A bold claim. During a conversation about connectivity on the move an executive at a leading public Wi-Fi provider told us cellular connectivity was no longer important. Expensive and slow, yes, but not required in most user cases, he said. This was because, he claimed, you can always find a public Wi-Fi network when you need to get online.

Such a claim requires testing, and testing is what we do here at PC Advisor.

We took to the streets to find out just how much connectivity there is to be found. We paired up with our friends at Broadband Genie and signed up to the three major public Wi-Fi networks, BT Wi-fi, O2 and The Cloud. Armed only with a laptop, we sent five testers on to the streets of London, setting them a series of timed web-based challenges, each to be completed at the same time in the same place.

The five contenders included three testers who were allowed only to use their chosen public Wi-Fi network, BT Wi-fi, O2 or The Cloud. We also had a wildcard tester who was signed up to no accounts, but able to use any public Wi-Fi network that didn't require direct payment. As a control we had one tester using 3G, with a dongle from Three (the winner of our recent best mobile network group test).

Some caveats: we tested in central London, which is unusually well covered by public Wi-Fi. This was to give the testers the best possible chance of success and because, well, we're based in London. Experience may differ in your area, although you'll see as we go along that the types of places in which you can get online can be found in most towns and cities. The rural experience is, of course, very different.

This was not a scientific test. To an extent it required ingenuity and flexibility on the part of the individual tester. Consider this more of an anecdotal piece: in part we wanted to test just how much thought was required to find a usable connection. The user experience is an important part of all consumer tech, after all.

It's unlikely that in real life a customer of, say, The Cloud would ignore a free BT connection and cast aside a working 3G network to find a Cloud hotspot. In reality, we would all take the most convenient option to get online, provided it was fit for purpose and unlikely to cost us more than the service for which we'd already paid. See also: The UK's best mobile networks revealed: mobile broadband group test.

Public Wi-Fi hotspot

How good is public Wi-Fi? How we tested

For each task each tester could use only the Wi-Fi service they'd been allocated, with the exception of the wildcard tester who could use only free public Wi-Fi. All the contenders started in the same place at the same time, then had to find the nearest wireless connection to complete the task we set.

It wasn't a competition as such, but an experiment to see how feasible it is to rely only on public internet. The contenders had 10 minutes to complete each task. If they couldn't do so, it was considered a failure.

The testers knew in advance which network was theirs to test, so they could research which third-party stores, bars and restaurants would likely offer a connection. They did not know the location or content of the tests, however, so couldn't plan ahead. See also: Android vs iPhone vs Windows Phone vs BlackBerry: which is the best phone to use on the move?

Public Wi-fi test 1. Read a book at the British Library

Starting from the yard outside the British Library, we asked our testers to find a web connection, search for the Project Gutenberg website and find Gulliver's Travels by Jonathan Swift. They then had to download and open the ePub (with images) file, and note the time in which they completed the task, and the location of the connection used.

Our O2 tester had previously signed up to O2 Wi-Fi and downloaded the app to their smartphone. Thus it was easy to find a hotspot in a nearby coffee shop. However, it was a lengthy and difficult process to get online. By the time the laptop was connected they had ran out of time to carry out the task.

Our BT tester had a similar experience with a better outcome. They thought the BT signup process could be more streamlined, with less personal data required. However, they were able to quickly and easily download the book in the public lobby of a local hotel.

Our The Cloud tester found several hotspots close by, including three just over the road. An initial attempt in a Pret A Manger was unsuccessful as the connection was saturated by the lunchtime rush. Our intrepid hack popped next door to a Pizza Express and managed to very quickly download the e-book while standing outside.

There they shared a connection with our wildcard, also nicking Wi-Fi without paying for even some dough balls. Our wildcard initially headed to Starbucks, but it being a café near two major rail stations found it rammed with customers. Our tester could get a flat white and the promise of own-brand internet access, but not a seat. And web access turned out to be false promise, as they couldn't get past the branded pop-up window.

Our wildcard tester ultimately downloaded the book from the same The Cloud network as our The Cloud specialist. Lesson learned: restaurants have better internet access than coffee shops, even if you're next door in the latter.

The 3G control downloaded the book in a couple of minutes without moving from the start point. (See also: What's the best mobile network? UK mobile broadband tested.)

Public Wi-fi test 2. Plan your route on the Tube

The TubeWe then descended to the platform at King's Cross Underground Station, and asked our testers to navigate to tfl.gov.uk and use the journey planner to plan a route to St Paul's. We were miles below ground level so the 3G dongle was a washout.

O2 supports Wi-Fi on the tube, via Virgin Media. On the underground platform our O2 tester was able to sign into the Virgin Media Wi-Fi for free with their O2 credentials. They then hopped online and planned the journey in around three minutes. Neither BT nor The Cloud could match this.

Initially things went well for our wildcard tester. As Virgin Media's Wi-Fi was easily accessible they could either pay for a day's access or log in via EE, Vodafone or – although a nearly hidden option – 02.

We wouldn't let them pay any cash, but as an O2 mobile customer we let them plump for this. Our tester entered their mobile number and was told to expect a text with further instructions. A text they wouldn't receive until we resurfaced at St Paul's Station. So near, and yet so far.

Public Wi-fi test 3. Learn history at St Paul's

St PaulsWe travelled down to the front of St Paul's Cathedral, where we asked our testers to find a web connection and search for a story on the BBC website entitled How St Paul's Cathedral survived the Blitz. Then we asked them to save the main image to the desktop. Needless to say finding the image was no problem for our 3G control, although it did take a minute or two to download.

Our O2 tester had a better time. Their laptop automatically connected to an O2 hotspot at Yo Sushi, without them having to move. They were able to find the BBC news article and download the image in about two minutes.

Our BT tester could only envy such success. They found a BT Openzone at a Starbucks, and even managed to surf to the BBC home page on another overloaded connection. However, when they could surf no further they closed the browser to start again and found they couldn't reconnect.

Our The Cloud tester found numerous hotspots within a close proximity. Like O2 they were able to get a reasonably good connection sitting on the steps of St Paul's.

There was an odd issue with Chrome, which threw up a strange login screen, and the usual Sky ID did not work. But a quick switch to Firefox and our tester was able to connect. However, they then had to re-register the laptop with The Cloud and this part of the process would not finish, leaving our tester hanging on the device management screen.

A quick switch to a smartphone allowed the The Cloud tester to complete the task in the time allotted. So the connectivity was good, but the user experience not. This was not an unfamiliar occurrence.

And what became of our wildcard tester? Like the other testers they could see many networks, and five were accessible from where they were standing. They simply sat down on the steps and logged on. They also found Starbucks' network overloaded with PowerPoint pitch presentations attached to pressing emails and Russian hair braiding videos from YouTube, but Yo Sushi's Wi-Fi was wide open and the task was completed in no time.

Public Wi-fi test 4. Find out what's on at Tate Modern

TATE MODERNAfter a brisk trot across the river (using a bridge) we found ourselves at the front of the Tate Modern gallery. The task here was simple: find a web connection, open the Tate Modern website and find the What's On page. It should have been simple, and it was for the 3G control test.

It was relatively simple for our O2 tester, too. Using the O2 app they located the nearest hotspot – a five-minute walk away at a local pub. The laptop automatically connected before our tester had even ordered a drink.

Our BT tester had a much tougher time. Right outside the Tate several different, but apparently usable, networks appeared: BT Wi-fi, BT Wi-fi with Fon and BT Openzone. Our tester opened their browser and was taken to a BT wireless page to log in. However, they couldn't sign into their account because it was the wrong kind of BT Wi-fi. A hop around the corner to a – yes – Starbucks solved this problem, but the sheer variety of 'BT' networks was baffling. Another example of the importance of the user experience as well as the connectivity.

Still, that experience beat The Cloud tester's. The smartphone app displayed a few hotspots in the area that seemed to be a short distance away, but our tester was not able to find them within the time limit. Fail.

Meanwhile, as their colleagues charged off in different directions to find their individual networks, our wildcard tester had cannily noticed that the Tate has its own Wi-Fi, so waited smugly for them to depart and logged on from the café (you have to drink a lot of coffee to surf on the move). Unfortunately, they couldn't connect, so our wildcard tester drank up and moved to a different floor. Again, no luck. There was time for only one more try but, again, nothing. Another fail.

NEXT PAGE: we watch the South Bank Show on the south bank of the river...