Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-41.co.uk. NS
Answer
awsdns-41.co.uk. 5 NS g-ns-1837.awsdns-41.co.uk.
awsdns-41.co.uk. 5 NS g-ns-361.awsdns-41.co.uk.
awsdns-41.co.uk. 5 NS g-ns-937.awsdns-41.co.uk.
awsdns-41.co.uk. 5 NS g-ns-1516.awsdns-41.co.uk.
Authority
The response has no authority records.
Additional
g-ns-361.awsdns-41.co.uk. 5 A 205.251.193.105
g-ns-937.awsdns-41.co.uk. 5 A 205.251.195.169
g-ns-1516.awsdns-41.co.uk. 5 A 205.251.197.236
g-ns-1837.awsdns-41.co.uk. 5 A 205.251.199.45
g-ns-361.awsdns-41.co.uk. 5 AAAA 2600:9000:5301:6900:0:0:0:1
g-ns-937.awsdns-41.co.uk. 5 AAAA 2600:9000:5303:a900:0:0:0:1
g-ns-1516.awsdns-41.co.uk. 5 AAAA 2600:9000:5305:ec00:0:0:0:1
g-ns-1837.awsdns-41.co.uk. 5 AAAA 2600:9000:5307:2d00:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0