Apex domains cannot have CNAME records.
Question and response
Question
dig jisc.ac.uk. NS
Answer
jisc.ac.uk. 5 NS ns12.ja.net.
jisc.ac.uk. 5 NS ns11.ja.net.
jisc.ac.uk. 5 NS ns10.ja.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0