Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-01.co.uk. NS
Answer
awsdns-01.co.uk. 5 NS g-ns-897.awsdns-01.co.uk.
awsdns-01.co.uk. 5 NS g-ns-321.awsdns-01.co.uk.
awsdns-01.co.uk. 5 NS g-ns-1797.awsdns-01.co.uk.
awsdns-01.co.uk. 5 NS g-ns-1476.awsdns-01.co.uk.
Authority
The response has no authority records.
Additional
g-ns-321.awsdns-01.co.uk. 5 A 205.251.193.65
g-ns-897.awsdns-01.co.uk. 5 A 205.251.195.129
g-ns-1476.awsdns-01.co.uk. 5 A 205.251.197.196
g-ns-1797.awsdns-01.co.uk. 5 A 205.251.199.5
g-ns-321.awsdns-01.co.uk. 5 AAAA 2600:9000:5301:4100:0:0:0:1
g-ns-897.awsdns-01.co.uk. 5 AAAA 2600:9000:5303:8100:0:0:0:1
g-ns-1476.awsdns-01.co.uk. 5 AAAA 2600:9000:5305:c400:0:0:0:1
g-ns-1797.awsdns-01.co.uk. 5 AAAA 2600:9000:5307:500:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0