Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-37.co.uk. NS
Answer
awsdns-37.co.uk. 5 NS g-ns-357.awsdns-37.co.uk.
awsdns-37.co.uk. 5 NS g-ns-1512.awsdns-37.co.uk.
awsdns-37.co.uk. 5 NS g-ns-933.awsdns-37.co.uk.
awsdns-37.co.uk. 5 NS g-ns-1833.awsdns-37.co.uk.
Authority
The response has no authority records.
Additional
g-ns-357.awsdns-37.co.uk. 5 A 205.251.193.101
g-ns-933.awsdns-37.co.uk. 5 A 205.251.195.165
g-ns-1512.awsdns-37.co.uk. 5 A 205.251.197.232
g-ns-1833.awsdns-37.co.uk. 5 A 205.251.199.41
g-ns-357.awsdns-37.co.uk. 5 AAAA 2600:9000:5301:6500:0:0:0:1
g-ns-933.awsdns-37.co.uk. 5 AAAA 2600:9000:5303:a500:0:0:0:1
g-ns-1512.awsdns-37.co.uk. 5 AAAA 2600:9000:5305:e800:0:0:0:1
g-ns-1833.awsdns-37.co.uk. 5 AAAA 2600:9000:5307:2900:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0