Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-39.co.uk. NS
Answer
awsdns-39.co.uk. 5 NS g-ns-359.awsdns-39.co.uk.
awsdns-39.co.uk. 5 NS g-ns-935.awsdns-39.co.uk.
awsdns-39.co.uk. 5 NS g-ns-1514.awsdns-39.co.uk.
awsdns-39.co.uk. 5 NS g-ns-1835.awsdns-39.co.uk.
Authority
The response has no authority records.
Additional
g-ns-359.awsdns-39.co.uk. 5 A 205.251.193.103
g-ns-935.awsdns-39.co.uk. 5 A 205.251.195.167
g-ns-1514.awsdns-39.co.uk. 5 A 205.251.197.234
g-ns-1835.awsdns-39.co.uk. 5 A 205.251.199.43
g-ns-359.awsdns-39.co.uk. 5 AAAA 2600:9000:5301:6700:0:0:0:1
g-ns-935.awsdns-39.co.uk. 5 AAAA 2600:9000:5303:a700:0:0:0:1
g-ns-1514.awsdns-39.co.uk. 5 AAAA 2600:9000:5305:ea00:0:0:0:1
g-ns-1835.awsdns-39.co.uk. 5 AAAA 2600:9000:5307:2b00:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0