Why do homes in the UK have separate hot and cold taps? (2018)

People tend to replace separate taps when they refurbish their bathrooms these because indeed there is no reason for them and they are not practical.

As for pull-cord switches, this is another "because that's the way others do, too" sort of thing. To have a normal switch in a bathroom is not explicitly forbidden and many electric safety regulations are poorly understood (ask 3 electricians about safety zones and you'll probably get 3 different answers) so people tend to cover their backsides by going over the top.

Here's another, more regional one: why do so many homes in England not have a lock on the bathroom door?

Having been born & raised in another part of the UK. I never saw a bathroom without a lock on the door til I moved to England. Where I'd say maybe half the homes I've been in don't.

Really cramps your style, when you're trying to go for a massive dump and your buttocks keep clenching up every time someone walks past the door!