Apex domains cannot have CNAME records.
Question and response
Question
dig optinet.co.uk. NS
Answer
optinet.co.uk. 5 NS ns14.domaincontrol.com.
optinet.co.uk. 5 NS ns13.domaincontrol.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0