Apex domains cannot have CNAME records.
Question and response
Question
dig extendcp.co.uk. NS
Answer
extendcp.co.uk. 5 NS ns-241-c.gandi.net.
extendcp.co.uk. 5 NS ns-24-b.gandi.net.
extendcp.co.uk. 5 NS ns-14-a.gandi.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0