Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-35.co.uk. NS
Answer
awsdns-35.co.uk. 5 NS g-ns-1510.awsdns-35.co.uk.
awsdns-35.co.uk. 5 NS g-ns-1831.awsdns-35.co.uk.
awsdns-35.co.uk. 5 NS g-ns-355.awsdns-35.co.uk.
awsdns-35.co.uk. 5 NS g-ns-931.awsdns-35.co.uk.
Authority
The response has no authority records.
Additional
g-ns-355.awsdns-35.co.uk. 5 A 205.251.193.99
g-ns-931.awsdns-35.co.uk. 5 A 205.251.195.163
g-ns-1510.awsdns-35.co.uk. 5 A 205.251.197.230
g-ns-1831.awsdns-35.co.uk. 5 A 205.251.199.39
g-ns-355.awsdns-35.co.uk. 5 AAAA 2600:9000:5301:6300:0:0:0:1
g-ns-931.awsdns-35.co.uk. 5 AAAA 2600:9000:5303:a300:0:0:0:1
g-ns-1510.awsdns-35.co.uk. 5 AAAA 2600:9000:5305:e600:0:0:0:1
g-ns-1831.awsdns-35.co.uk. 5 AAAA 2600:9000:5307:2700:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0