Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-61.co.uk. NS
Answer
awsdns-61.co.uk. 5 NS g-ns-1217.awsdns-61.co.uk.
awsdns-61.co.uk. 5 NS g-ns-1538.awsdns-61.co.uk.
awsdns-61.co.uk. 5 NS g-ns-381.awsdns-61.co.uk.
awsdns-61.co.uk. 5 NS g-ns-957.awsdns-61.co.uk.
Authority
The response has no authority records.
Additional
g-ns-381.awsdns-61.co.uk. 5 A 205.251.193.125
g-ns-957.awsdns-61.co.uk. 5 A 205.251.195.189
g-ns-1217.awsdns-61.co.uk. 5 A 205.251.196.193
g-ns-1538.awsdns-61.co.uk. 5 A 205.251.198.2
g-ns-381.awsdns-61.co.uk. 5 AAAA 2600:9000:5301:7d00:0:0:0:1
g-ns-957.awsdns-61.co.uk. 5 AAAA 2600:9000:5303:bd00:0:0:0:1
g-ns-1217.awsdns-61.co.uk. 5 AAAA 2600:9000:5304:c100:0:0:0:1
g-ns-1538.awsdns-61.co.uk. 5 AAAA 2600:9000:5306:200:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0