Apex domains cannot have CNAME records.
Question and response
Question
dig dnsever.co.uk. NS
Answer
dnsever.co.uk. 5 NS ns3.dnsever.net.
dnsever.co.uk. 5 NS ns3.dnsever.org.
dnsever.co.uk. 5 NS ns3.dnsever.com.
dnsever.co.uk. 5 NS ns3.dnsever.co.uk.
dnsever.co.uk. 5 NS ns3.dnsever.co.kr.
Authority
The response has no authority records.
Additional
ns3.dnsever.co.uk. 5 A 15.235.3.172
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0