Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-52.co.uk. NS
Answer
awsdns-52.co.uk. 3 NS g-ns-1848.awsdns-52.co.uk.
awsdns-52.co.uk. 3 NS g-ns-948.awsdns-52.co.uk.
awsdns-52.co.uk. 3 NS g-ns-372.awsdns-52.co.uk.
awsdns-52.co.uk. 3 NS g-ns-1527.awsdns-52.co.uk.
Authority
The response has no authority records.
Additional
g-ns-372.awsdns-52.co.uk. 3 A 205.251.193.116
g-ns-948.awsdns-52.co.uk. 3 A 205.251.195.180
g-ns-1527.awsdns-52.co.uk. 3 A 205.251.197.247
g-ns-1848.awsdns-52.co.uk. 3 A 205.251.199.56
g-ns-372.awsdns-52.co.uk. 3 AAAA 2600:9000:5301:7400:0:0:0:1
g-ns-948.awsdns-52.co.uk. 3 AAAA 2600:9000:5303:b400:0:0:0:1
g-ns-1527.awsdns-52.co.uk. 3 AAAA 2600:9000:5305:f700:0:0:0:1
g-ns-1848.awsdns-52.co.uk. 3 AAAA 2600:9000:5307:3800:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0