Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-50.co.uk. NS
Answer
awsdns-50.co.uk. 5 NS g-ns-370.awsdns-50.co.uk.
awsdns-50.co.uk. 5 NS g-ns-1525.awsdns-50.co.uk.
awsdns-50.co.uk. 5 NS g-ns-946.awsdns-50.co.uk.
awsdns-50.co.uk. 5 NS g-ns-1846.awsdns-50.co.uk.
Authority
The response has no authority records.
Additional
g-ns-370.awsdns-50.co.uk. 5 A 205.251.193.114
g-ns-946.awsdns-50.co.uk. 5 A 205.251.195.178
g-ns-1525.awsdns-50.co.uk. 5 A 205.251.197.245
g-ns-1846.awsdns-50.co.uk. 5 A 205.251.199.54
g-ns-370.awsdns-50.co.uk. 5 AAAA 2600:9000:5301:7200:0:0:0:1
g-ns-946.awsdns-50.co.uk. 5 AAAA 2600:9000:5303:b200:0:0:0:1
g-ns-1525.awsdns-50.co.uk. 5 AAAA 2600:9000:5305:f500:0:0:0:1
g-ns-1846.awsdns-50.co.uk. 5 AAAA 2600:9000:5307:3600:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0