Apex domains cannot have CNAME records.
Question and response
Question
dig ncuk.net. NS
Answer
ncuk.net. 5 NS ns4.ncuk.net.uk.
ncuk.net. 5 NS ns1.ncuk.net.
ncuk.net. 5 NS ns2.ncuk.net.
ncuk.net. 5 NS ns0.ncuk.net.
ncuk.net. 5 NS ns3.ncuk.net.uk.
ncuk.net. 5 NS ns5.ncuk.net.uk.
Authority
The response has no authority records.
Additional
ns0.ncuk.net. 5 A 80.249.96.5
ns1.ncuk.net. 5 A 93.186.35.5
ns2.ncuk.net. 5 A 144.76.65.244
ns0.ncuk.net. 5 AAAA 2a02:68:0:1110:0:0:0:0
ns2.ncuk.net. 5 AAAA 2a01:4f8:191:74da:0:0:0:5
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0