In the UK Nominet (the UK domain namr registrar - nic.uk) only permitted 3rd domains - co.uk. org.uk, me.uk. then there were "prove your status" ones such as ltd.uk, plc.uk and ac.uk plus ones like gov.uk, mod.uk, sch.uk, nhs.uk etc.

.uk was opened up relatively recently.

I own a .uk and it still feels weird not having something in-between.