Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-45.co.uk. NS
Answer
awsdns-45.co.uk. 5 NS g-ns-1841.awsdns-45.co.uk.
awsdns-45.co.uk. 5 NS g-ns-1520.awsdns-45.co.uk.
awsdns-45.co.uk. 5 NS g-ns-365.awsdns-45.co.uk.
awsdns-45.co.uk. 5 NS g-ns-941.awsdns-45.co.uk.
Authority
The response has no authority records.
Additional
g-ns-365.awsdns-45.co.uk. 5 A 205.251.193.109
g-ns-941.awsdns-45.co.uk. 5 A 205.251.195.173
g-ns-1520.awsdns-45.co.uk. 5 A 205.251.197.240
g-ns-1841.awsdns-45.co.uk. 5 A 205.251.199.49
g-ns-365.awsdns-45.co.uk. 5 AAAA 2600:9000:5301:6d00:0:0:0:1
g-ns-941.awsdns-45.co.uk. 5 AAAA 2600:9000:5303:ad00:0:0:0:1
g-ns-1520.awsdns-45.co.uk. 5 AAAA 2600:9000:5305:f000:0:0:0:1
g-ns-1841.awsdns-45.co.uk. 5 AAAA 2600:9000:5307:3100:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0