Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-55.co.uk. NS
Answer
awsdns-55.co.uk. 5 NS g-ns-1530.awsdns-55.co.uk.
awsdns-55.co.uk. 5 NS g-ns-1851.awsdns-55.co.uk.
awsdns-55.co.uk. 5 NS g-ns-375.awsdns-55.co.uk.
awsdns-55.co.uk. 5 NS g-ns-951.awsdns-55.co.uk.
Authority
The response has no authority records.
Additional
g-ns-375.awsdns-55.co.uk. 5 A 205.251.193.119
g-ns-951.awsdns-55.co.uk. 5 A 205.251.195.183
g-ns-1530.awsdns-55.co.uk. 5 A 205.251.197.250
g-ns-1851.awsdns-55.co.uk. 5 A 205.251.199.59
g-ns-375.awsdns-55.co.uk. 5 AAAA 2600:9000:5301:7700:0:0:0:1
g-ns-951.awsdns-55.co.uk. 5 AAAA 2600:9000:5303:b700:0:0:0:1
g-ns-1530.awsdns-55.co.uk. 5 AAAA 2600:9000:5305:fa00:0:0:0:1
g-ns-1851.awsdns-55.co.uk. 5 AAAA 2600:9000:5307:3b00:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0