Appalling? In contrast to what countries? From the countries I've been to, the UK has one of the best standards of driving, including in their ability.
For instance, a country like Jamaica (many 3rd world countries I've been to are somewhat similar), has bad roads (lots of pot holes etc.) and maniac drivers, who overtake almost hitting on-coming traffic, and do whatever they please. The drivers are good in the sense they don't crash their cars. But bad in the sense they break rules.
Then over to the US. Okay, they don't drive like maniacs (except on those traffic cops TV shows). But they have massive straight roads, automatic cars, even a 5 year old could drive there.
With the UK, especially driving in built up places like London, requires another level of skill due to driving manual cars, lots of winding/spaghetti like narrow-roads, lots of congestion prompting you to drive down back roads, complex layers of traffic rules (red routes, parking restrictions, bus lanes, speed cameras), one needs to know these like the back of their hand to get from A to B in efficient time.
We also have one of the lowest fatality rates on our roads. I think only Ireland is safer.