Apex domains cannot have CNAME records.
Question and response
Question
dig amzndns.co.uk. NS
Answer
amzndns.co.uk. 5 NS g-ns4.amzndns.co.uk.
amzndns.co.uk. 5 NS g-ns3.amzndns.co.uk.
amzndns.co.uk. 5 NS g-ns1.amzndns.co.uk.
amzndns.co.uk. 5 NS g-ns2.amzndns.co.uk.
Authority
The response has no authority records.
Additional
g-ns1.amzndns.co.uk. 5 A 205.251.196.59
g-ns2.amzndns.co.uk. 5 A 205.251.192.126
g-ns3.amzndns.co.uk. 5 A 205.251.195.158
g-ns4.amzndns.co.uk. 5 A 205.251.198.44
g-ns1.amzndns.co.uk. 5 AAAA 2600:9000:5304:3b00:0:0:0:1
g-ns2.amzndns.co.uk. 5 AAAA 2600:9000:5300:7e00:0:0:0:1
g-ns3.amzndns.co.uk. 5 AAAA 2600:9000:5303:9e00:0:0:0:1
g-ns4.amzndns.co.uk. 5 AAAA 2600:9000:5306:2c00:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0