Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-05.co.uk. NS
Answer
awsdns-05.co.uk. 5 NS g-ns-1801.awsdns-05.co.uk.
awsdns-05.co.uk. 5 NS g-ns-901.awsdns-05.co.uk.
awsdns-05.co.uk. 5 NS g-ns-325.awsdns-05.co.uk.
awsdns-05.co.uk. 5 NS g-ns-1480.awsdns-05.co.uk.
Authority
The response has no authority records.
Additional
g-ns-325.awsdns-05.co.uk. 5 A 205.251.193.69
g-ns-901.awsdns-05.co.uk. 5 A 205.251.195.133
g-ns-1480.awsdns-05.co.uk. 5 A 205.251.197.200
g-ns-1801.awsdns-05.co.uk. 5 A 205.251.199.9
g-ns-325.awsdns-05.co.uk. 5 AAAA 2600:9000:5301:4500:0:0:0:1
g-ns-901.awsdns-05.co.uk. 5 AAAA 2600:9000:5303:8500:0:0:0:1
g-ns-1480.awsdns-05.co.uk. 5 AAAA 2600:9000:5305:c800:0:0:0:1
g-ns-1801.awsdns-05.co.uk. 5 AAAA 2600:9000:5307:900:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0