Even .org.uk isn't foolproof; I've had mine for 20 years and still occasionally get people leaving off the .uk. The most recent suspect is Google Android keyboard will autocomplete my email address .. and leave off the ".uk"!
Like many countries, .UK had a second-level set of categories for different types of organization. There's also .net.uk, .sch.uk, .ac.uk, .gov.uk, .nhs.uk, .mod.uk, .police.uk, ...
.AU, .NZ, .JP, .MX, .BR, .TH... it's not uncommon.