Apex domains cannot have CNAME records.
Question and response
Question
dig ic.ac.uk. NS
Answer
ic.ac.uk. 3 NS ns2.ic.ac.uk.
ic.ac.uk. 3 NS ns0.ic.ac.uk.
ic.ac.uk. 3 NS ns1.ic.ac.uk.
ic.ac.uk. 3 NS auth0.dns.cam.ac.uk.
Authority
The response has no authority records.
Additional
ns0.ic.ac.uk. 3 A 155.198.142.80
ns1.ic.ac.uk. 3 A 155.198.142.81
ns2.ic.ac.uk. 3 A 155.198.142.82
auth0.dns.cam.ac.uk. 4 A 131.111.8.37
ns0.ic.ac.uk. 3 AAAA 2a0c:5bc0:4:1:0:0:0:80
ns1.ic.ac.uk. 3 AAAA 2a0c:5bc0:4:1:0:0:0:81
ns2.ic.ac.uk. 3 AAAA 2a0c:5bc0:4:1:0:0:0:82
auth0.dns.cam.ac.uk. 4 AAAA 2001:630:212:8:0:0:d:a0
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0