Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-22.co.uk. NS
Answer
awsdns-22.co.uk. 5 NS g-ns-1818.awsdns-22.co.uk.
awsdns-22.co.uk. 5 NS g-ns-918.awsdns-22.co.uk.
awsdns-22.co.uk. 5 NS g-ns-342.awsdns-22.co.uk.
awsdns-22.co.uk. 5 NS g-ns-1497.awsdns-22.co.uk.
Authority
The response has no authority records.
Additional
g-ns-342.awsdns-22.co.uk. 5 A 205.251.193.86
g-ns-918.awsdns-22.co.uk. 5 A 205.251.195.150
g-ns-1497.awsdns-22.co.uk. 5 A 205.251.197.217
g-ns-1818.awsdns-22.co.uk. 5 A 205.251.199.26
g-ns-342.awsdns-22.co.uk. 5 AAAA 2600:9000:5301:5600:0:0:0:1
g-ns-918.awsdns-22.co.uk. 5 AAAA 2600:9000:5303:9600:0:0:0:1
g-ns-1497.awsdns-22.co.uk. 5 AAAA 2600:9000:5305:d900:0:0:0:1
g-ns-1818.awsdns-22.co.uk. 5 AAAA 2600:9000:5307:1a00:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0