Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-53.co.uk. NS
Answer
awsdns-53.co.uk. 5 NS g-ns-949.awsdns-53.co.uk.
awsdns-53.co.uk. 5 NS g-ns-373.awsdns-53.co.uk.
awsdns-53.co.uk. 5 NS g-ns-1849.awsdns-53.co.uk.
awsdns-53.co.uk. 5 NS g-ns-1528.awsdns-53.co.uk.
Authority
The response has no authority records.
Additional
g-ns-373.awsdns-53.co.uk. 5 A 205.251.193.117
g-ns-949.awsdns-53.co.uk. 5 A 205.251.195.181
g-ns-1528.awsdns-53.co.uk. 5 A 205.251.197.248
g-ns-1849.awsdns-53.co.uk. 5 A 205.251.199.57
g-ns-373.awsdns-53.co.uk. 5 AAAA 2600:9000:5301:7500:0:0:0:1
g-ns-949.awsdns-53.co.uk. 5 AAAA 2600:9000:5303:b500:0:0:0:1
g-ns-1528.awsdns-53.co.uk. 5 AAAA 2600:9000:5305:f800:0:0:0:1
g-ns-1849.awsdns-53.co.uk. 5 AAAA 2600:9000:5307:3900:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0