Apex domains cannot have CNAME records.
Question and response
Question
dig userve.uk. NS
Answer
userve.uk. 5 NS ns.userve.uk.
userve.uk. 5 NS ns2.userve.net.
userve.uk. 5 NS ns.userve.net.
Authority
The response has no authority records.
Additional
ns.userve.uk. 5 A 52.137.22.17
ns.userve.net. 5 A 217.196.1.5
ns2.userve.net. 5 A 217.196.1.6
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0