Apex domains cannot have CNAME records.
Question and response
Question
dig cloudns.uk. NS
Answer
cloudns.uk. 3 NS pns2.cloudns.com.
cloudns.uk. 3 NS pns1.cloudns.net.
cloudns.uk. 3 NS ns2.cloudns.com.
cloudns.uk. 3 NS pns3.cloudns.net.
cloudns.uk. 3 NS pns64.cloudns.uk.
Authority
The response has no authority records.
Additional
pns1.cloudns.net. 3 A 185.136.96.111
pns2.cloudns.com. 3 A 185.136.97.111
pns64.cloudns.uk. 3 A 45.83.251.16
pns1.cloudns.net. 3 AAAA 2a06:fb00:1:0:0:0:1:111
pns2.cloudns.com. 3 AAAA 2a06:fb00:1:0:0:0:2:111
pns64.cloudns.uk. 3 AAAA 2a06:fb00:2:0:0:0:4:16
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0