In the UK, we use a mix.
In education, you are taught to use all metric units for mass, lengths and volume.
In everyday life , it's different. We use miles and yards for all our road signs and car speeds. For shorter distances, it's usually m in conversation. We use the metric system for weights most of the time, but some people still like referring to mass in stone and pounds. For milk we use pints as the predominant measure, with litres underneath. But, for all other liquids the metric system is used i.e. ml/l. Lengths are commonly measured in both but mostly in m. But, we definitely use celsius for temperature. It's easy. 0 is freezing. 100 is boiling. It snows around/above the 0 point. It freezes when we get to negative. Easy. Around 10 is average. Latter teens to 20 is where it gets hot.
Also, scaling in 10's and 100's is the easiest thing in the world. It is a bit of a shame we don't use km, km/h and m for road measurements.
