Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-24.co.uk. NS
Answer
awsdns-24.co.uk. 1 NS g-ns-1820.awsdns-24.co.uk.
awsdns-24.co.uk. 1 NS g-ns-920.awsdns-24.co.uk.
awsdns-24.co.uk. 1 NS g-ns-344.awsdns-24.co.uk.
awsdns-24.co.uk. 1 NS g-ns-1499.awsdns-24.co.uk.
Authority
The response has no authority records.
Additional
g-ns-344.awsdns-24.co.uk. 1 A 205.251.193.88
g-ns-920.awsdns-24.co.uk. 1 A 205.251.195.152
g-ns-1499.awsdns-24.co.uk. 1 A 205.251.197.219
g-ns-1820.awsdns-24.co.uk. 1 A 205.251.199.28
g-ns-344.awsdns-24.co.uk. 1 AAAA 2600:9000:5301:5800:0:0:0:1
g-ns-920.awsdns-24.co.uk. 1 AAAA 2600:9000:5303:9800:0:0:0:1
g-ns-1499.awsdns-24.co.uk. 1 AAAA 2600:9000:5305:db00:0:0:0:1
g-ns-1820.awsdns-24.co.uk. 1 AAAA 2600:9000:5307:1c00:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0