Apex domains cannot have CNAME records.
Question and response
Question
dig longstonebarn.co.uk. NS
Answer
longstonebarn.co.uk. 5 NS ns-46.awsdns-05.com.
longstonebarn.co.uk. 5 NS ns-1424.awsdns-50.org.
longstonebarn.co.uk. 5 NS ns-1763.awsdns-28.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0