Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-00.co.uk. NS
Answer
awsdns-00.co.uk. 5 NS g-ns-896.awsdns-00.co.uk.
awsdns-00.co.uk. 5 NS g-ns-1475.awsdns-00.co.uk.
awsdns-00.co.uk. 5 NS g-ns-1796.awsdns-00.co.uk.
awsdns-00.co.uk. 5 NS g-ns-320.awsdns-00.co.uk.
Authority
The response has no authority records.
Additional
g-ns-320.awsdns-00.co.uk. 5 A 205.251.193.64
g-ns-896.awsdns-00.co.uk. 5 A 205.251.195.128
g-ns-1475.awsdns-00.co.uk. 5 A 205.251.197.195
g-ns-1796.awsdns-00.co.uk. 5 A 205.251.199.4
g-ns-320.awsdns-00.co.uk. 5 AAAA 2600:9000:5301:4000:0:0:0:1
g-ns-896.awsdns-00.co.uk. 5 AAAA 2600:9000:5303:8000:0:0:0:1
g-ns-1475.awsdns-00.co.uk. 5 AAAA 2600:9000:5305:c300:0:0:0:1
g-ns-1796.awsdns-00.co.uk. 5 AAAA 2600:9000:5307:400:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0