Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-13.co.uk. NS
Answer
awsdns-13.co.uk. 5 NS g-ns-1809.awsdns-13.co.uk.
awsdns-13.co.uk. 5 NS g-ns-333.awsdns-13.co.uk.
awsdns-13.co.uk. 5 NS g-ns-909.awsdns-13.co.uk.
awsdns-13.co.uk. 5 NS g-ns-1488.awsdns-13.co.uk.
Authority
The response has no authority records.
Additional
g-ns-333.awsdns-13.co.uk. 5 A 205.251.193.77
g-ns-909.awsdns-13.co.uk. 5 A 205.251.195.141
g-ns-1488.awsdns-13.co.uk. 5 A 205.251.197.208
g-ns-1809.awsdns-13.co.uk. 5 A 205.251.199.17
g-ns-333.awsdns-13.co.uk. 5 AAAA 2600:9000:5301:4d00:0:0:0:1
g-ns-909.awsdns-13.co.uk. 5 AAAA 2600:9000:5303:8d00:0:0:0:1
g-ns-1488.awsdns-13.co.uk. 5 AAAA 2600:9000:5305:d000:0:0:0:1
g-ns-1809.awsdns-13.co.uk. 5 AAAA 2600:9000:5307:1100:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0