Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-27.co.uk. NS
Answer
awsdns-27.co.uk. 5 NS g-ns-1823.awsdns-27.co.uk.
awsdns-27.co.uk. 5 NS g-ns-923.awsdns-27.co.uk.
awsdns-27.co.uk. 5 NS g-ns-347.awsdns-27.co.uk.
awsdns-27.co.uk. 5 NS g-ns-1502.awsdns-27.co.uk.
Authority
The response has no authority records.
Additional
g-ns-347.awsdns-27.co.uk. 5 A 205.251.193.91
g-ns-923.awsdns-27.co.uk. 5 A 205.251.195.155
g-ns-1502.awsdns-27.co.uk. 5 A 205.251.197.222
g-ns-1823.awsdns-27.co.uk. 5 A 205.251.199.31
g-ns-347.awsdns-27.co.uk. 5 AAAA 2600:9000:5301:5b00:0:0:0:1
g-ns-923.awsdns-27.co.uk. 5 AAAA 2600:9000:5303:9b00:0:0:0:1
g-ns-1502.awsdns-27.co.uk. 5 AAAA 2600:9000:5305:de00:0:0:0:1
g-ns-1823.awsdns-27.co.uk. 5 AAAA 2600:9000:5307:1f00:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0