Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-29.co.uk. NS
Answer
awsdns-29.co.uk. 5 NS g-ns-349.awsdns-29.co.uk.
awsdns-29.co.uk. 5 NS g-ns-1504.awsdns-29.co.uk.
awsdns-29.co.uk. 5 NS g-ns-925.awsdns-29.co.uk.
awsdns-29.co.uk. 5 NS g-ns-1825.awsdns-29.co.uk.
Authority
The response has no authority records.
Additional
g-ns-349.awsdns-29.co.uk. 5 A 205.251.193.93
g-ns-925.awsdns-29.co.uk. 5 A 205.251.195.157
g-ns-1504.awsdns-29.co.uk. 5 A 205.251.197.224
g-ns-1825.awsdns-29.co.uk. 5 A 205.251.199.33
g-ns-349.awsdns-29.co.uk. 5 AAAA 2600:9000:5301:5d00:0:0:0:1
g-ns-925.awsdns-29.co.uk. 5 AAAA 2600:9000:5303:9d00:0:0:0:1
g-ns-1504.awsdns-29.co.uk. 5 AAAA 2600:9000:5305:e000:0:0:0:1
g-ns-1825.awsdns-29.co.uk. 5 AAAA 2600:9000:5307:2100:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0