Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-17.co.uk. NS
Answer
awsdns-17.co.uk. 5 NS g-ns-913.awsdns-17.co.uk.
awsdns-17.co.uk. 5 NS g-ns-337.awsdns-17.co.uk.
awsdns-17.co.uk. 5 NS g-ns-1813.awsdns-17.co.uk.
awsdns-17.co.uk. 5 NS g-ns-1492.awsdns-17.co.uk.
Authority
The response has no authority records.
Additional
g-ns-337.awsdns-17.co.uk. 5 A 205.251.193.81
g-ns-913.awsdns-17.co.uk. 5 A 205.251.195.145
g-ns-1492.awsdns-17.co.uk. 5 A 205.251.197.212
g-ns-1813.awsdns-17.co.uk. 5 A 205.251.199.21
g-ns-337.awsdns-17.co.uk. 5 AAAA 2600:9000:5301:5100:0:0:0:1
g-ns-913.awsdns-17.co.uk. 5 AAAA 2600:9000:5303:9100:0:0:0:1
g-ns-1492.awsdns-17.co.uk. 5 AAAA 2600:9000:5305:d400:0:0:0:1
g-ns-1813.awsdns-17.co.uk. 5 AAAA 2600:9000:5307:1500:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0