Apex domains cannot have CNAME records.
Question and response
Question
dig toob.co.uk. NS
Answer
toob.co.uk. 5 NS ns2.toob.co.uk.
toob.co.uk. 5 NS pdns06.domaincontrol.com.
toob.co.uk. 5 NS ns1.toob.co.uk.
toob.co.uk. 5 NS pdns05.domaincontrol.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0