Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-04.co.uk. NS
Answer
awsdns-04.co.uk. 5 NS g-ns-1479.awsdns-04.co.uk.
awsdns-04.co.uk. 5 NS g-ns-900.awsdns-04.co.uk.
awsdns-04.co.uk. 5 NS g-ns-324.awsdns-04.co.uk.
awsdns-04.co.uk. 5 NS g-ns-1800.awsdns-04.co.uk.
Authority
The response has no authority records.
Additional
g-ns-324.awsdns-04.co.uk. 5 A 205.251.193.68
g-ns-900.awsdns-04.co.uk. 5 A 205.251.195.132
g-ns-1479.awsdns-04.co.uk. 5 A 205.251.197.199
g-ns-1800.awsdns-04.co.uk. 5 A 205.251.199.8
g-ns-324.awsdns-04.co.uk. 5 AAAA 2600:9000:5301:4400:0:0:0:1
g-ns-900.awsdns-04.co.uk. 5 AAAA 2600:9000:5303:8400:0:0:0:1
g-ns-1479.awsdns-04.co.uk. 5 AAAA 2600:9000:5305:c700:0:0:0:1
g-ns-1800.awsdns-04.co.uk. 5 AAAA 2600:9000:5307:800:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0