Updated October 5: The latest OpenSignal/Which? report on UK mobile speeds has been released. The most notable change is that EE has retaken the performance crown from Three. All of the UK's mobile operators have seen big jumps in 4G LTE download speeds this year, though, which is a good sign. Coverage remains spotty, however.

Original story (April 2016)

4G LTE coverage in the UK, you will be unsurprised to hear, isn't very good, according to a new study by Which? and OpenSignal. As of January 2016, overall LTE coverage in the UK across the four mobile carriers was 53 percent, which puts the UK behind most of east Asia, northern Europe, and massive countries like China and the US. South Korea, the world leader, is sitting at 97 percent LTE coverage.

On the download speed front, things are a little better in the UK—especially for Three. Over the last six months, according to OpenSignal's data, Three has managed to boost its average 4G LTE download speed from 12Mbps to 18.7Mbps—a statistical tie with EE, which is sitting on 17.8Mbps. This is almost certainly due to Three ploughing more spectrum into its LTE network in the back half of 2015. Vodafone and O2 share a distant third place at around 12Mbps.

Three's LTE coverage (40 percent) is still far worse than EE (60 percent), though, which means Three users will often drop down to a 3G connection. Three's 3G network is the fastest in the UK according to OpenSignal, averaging 4.91Mbps—but EE's isn't far behind at 4Mbps (Vodafone is at 4.4Mbps, O2 is at 3Mbps).

How accurate is the data?

OpenSignal gathers mobile connection data from hundreds of thousands of users around the world who have downloaded the OpenSignal app. In the case of the latest UK report, OpenSignal says that 31,525 app users in the UK produced 60 million data points between November 2015 and January 2016. That's a pretty decent corpus of data, but probably not enough to get a good idea of coverage/speeds across all of rural Britain.

OpenSignal's "coverage" metric refers to time coverage, rather than geographic or population coverage. As in, the app measures how long—in seconds and minutes—you are connected to an LTE signal. OpenSignal says this gives a more "user-centric" view of coverage. For what it's worth, EE claims to have 95 percent coverage of the UK population, which is rather at odds with OpenSignal's measurement of 60 percent.

Because overall LTE coverage is so low in the UK, OpenSignal's latest data mainly points to one conclusion: try to pick a mobile carrier that has good LTE coverage in your town or city. OpenSignal has a tool for checking 3G and 4G coverage all over the world: try it out.

Why is the UK's LTE coverage so crap?

The chart above shows OpenSignal's measured LTE coverage for 68 countries as of February 2016, with the UK in 55th place. This is just one metric from one source of data so we should take it with a pinch of salt. But still, assuming that OpenSignal hasn't made a series of grievous statistical errors, it is quite remarkable that the UK is so far behind countries like the Netherlands (84 percent LTE coverage), which are similar in size and population density—or absolutely massive countries like China (76 percent) and the US (81 percent). Everyone pales in comparison to South Korea, which is sitting at 97 percent LTE coverage.

It is worth noting that the UK is ahead of France (51 percent) and Ireland (44 percent), and just behind Italy (57 percent) and Germany (56 percent)—so we're not the only country that is lagging.

But why is the UK so far behind? It's hard to say. One option is that the country's mobile carriers are still wary after the massively expensive 3G spectrum auction at the turn of the millennium, followed by the giant telecoms crash in 2001. Another option is that, after spending so much on rolling out 3G in the mid-2000s, the carriers aren't in a rush to spend more money on LTE infrastructure. That may change now that EE and Three are pushing hard into 4G LTE. The outcome of the planned Three-O2 merger may be significant, too, as the merged company would have more spectrum to play with.