A bit more digging about .uk names finds that:-
"At 08:00hrs on 10 June 2014 we launched the new shorter, sharper domain name .uk into our UK domain family. If you are an existing customer and own a unique .co.uk, .org.uk, .me.uk, .net.uk, .plc.uk or .ltd.uk, a .uk domain name may already have been reserved especially for you until 10 June 2019."
So... since apparently acme.co.uk was already registered at that time, acme.uk is reserved for the owner of that domain until 10 June 2019 (put the date in the diary, folks!).
I guess psyclist.uk was available because psyclist.co.uk wasn't registered on 10th June 2014.