Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-36.co.uk. NS
Answer
awsdns-36.co.uk. 5 NS g-ns-1832.awsdns-36.co.uk.
awsdns-36.co.uk. 5 NS g-ns-356.awsdns-36.co.uk.
awsdns-36.co.uk. 5 NS g-ns-932.awsdns-36.co.uk.
awsdns-36.co.uk. 5 NS g-ns-1511.awsdns-36.co.uk.
Authority
The response has no authority records.
Additional
g-ns-356.awsdns-36.co.uk. 5 A 205.251.193.100
g-ns-932.awsdns-36.co.uk. 5 A 205.251.195.164
g-ns-1511.awsdns-36.co.uk. 5 A 205.251.197.231
g-ns-1832.awsdns-36.co.uk. 5 A 205.251.199.40
g-ns-356.awsdns-36.co.uk. 5 AAAA 2600:9000:5301:6400:0:0:0:1
g-ns-932.awsdns-36.co.uk. 5 AAAA 2600:9000:5303:a400:0:0:0:1
g-ns-1511.awsdns-36.co.uk. 5 AAAA 2600:9000:5305:e700:0:0:0:1
g-ns-1832.awsdns-36.co.uk. 5 AAAA 2600:9000:5307:2800:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0