both Z wave and zigbee devices are popular in the UK, but you don’t buy them from everyday brick and mortar stores
Zwave is very popular in Europe. Vera is probably The most popular zwave controller, but Fibaro is also big. And Zipato is also well known. But the devices aren’t bought on the high street: these days they’re almost all bought online. 
Vesternet is one of the biggest online home automation retailers in the EU: take a look at their selection:
Zigbee is extremely popular in Europe for lighting (remember both Philips and Osram are EU companies). And there are a whole selection of brands for professionally installed zigbee systems there.
The main difference is that safety codes in many EU countries limit the amount of wiring that a non-electrician is legally allowed to do, even in their own home. (But that’s one of the main reasons that Phillips created the whole Hue LINE to begin with: to come up with Lighting systems that don’t require re-wiring.)
Finally, the big EU telco companies sell installed home automation systems which typically use Z wave or zigbee.
So in general the same protocols are popular, but you buy them from different sources than you would in the US.
( also, it’s true that zwave operates on a different frequency in Europe then it does in the US. But that’s not that big a deal because normally the only ones sold in a region will be the ones that work in that region.
https://products.z-wavealliance.org
)
The “home automation retailers“ thread in this forum lists both US and UK dealers.
FAQ: List of Home Automation Retailers
Amazon increasing the zigbee market in both the US and the UK
As I’ve mentioned before, now that Amazon is including a zigbee coordinator in both the echo plus and the echo show units (for both the US and the UK) I expect to see many more zigbee devices in both markets, and they are easy to find by going to the echo plus page on Amazon and then looking for the link to the list of compatible “simple setup” devices. Those will all be zigbee. 
Here’s the UK page:
Other protocols
Lightwave RF is a proprietary protocol and does not require a neutral wire, so it has become quite popular in the UK specifically. Sort of the equivalent of Lutron in the US. But there’s no official lightwave RF/SmartThings integration except through IFTTT.
As @bobbles notes below, you can set up an additional device as a server to be a “man in the middle“ and get a SmartThings integration that way. See the following thread: