Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-38.co.uk. NS
Answer
awsdns-38.co.uk. 5 NS g-ns-1513.awsdns-38.co.uk.
awsdns-38.co.uk. 5 NS g-ns-934.awsdns-38.co.uk.
awsdns-38.co.uk. 5 NS g-ns-358.awsdns-38.co.uk.
awsdns-38.co.uk. 5 NS g-ns-1834.awsdns-38.co.uk.
Authority
The response has no authority records.
Additional
g-ns-358.awsdns-38.co.uk. 5 A 205.251.193.102
g-ns-934.awsdns-38.co.uk. 5 A 205.251.195.166
g-ns-1513.awsdns-38.co.uk. 5 A 205.251.197.233
g-ns-1834.awsdns-38.co.uk. 5 A 205.251.199.42
g-ns-358.awsdns-38.co.uk. 5 AAAA 2600:9000:5301:6600:0:0:0:1
g-ns-934.awsdns-38.co.uk. 5 AAAA 2600:9000:5303:a600:0:0:0:1
g-ns-1513.awsdns-38.co.uk. 5 AAAA 2600:9000:5305:e900:0:0:0:1
g-ns-1834.awsdns-38.co.uk. 5 AAAA 2600:9000:5307:2a00:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0