Apex domains cannot have CNAME records.
Question and response
Question
dig hosts.co.uk. NS
Answer
hosts.co.uk. 5 NS ns1.phase8.net.
hosts.co.uk. 5 NS ns2.phase8.net.
hosts.co.uk. 5 NS ns0.phase8.net.
Authority
The response has no authority records.
Additional
ns0.phase8.net. 5 A 81.88.63.114
ns1.phase8.net. 5 A 85.233.160.68
ns2.phase8.net. 5 A 91.186.2.48
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0