Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-57.co.uk. NS
Answer
awsdns-57.co.uk. 5 NS g-ns-1853.awsdns-57.co.uk.
awsdns-57.co.uk. 5 NS g-ns-1532.awsdns-57.co.uk.
awsdns-57.co.uk. 5 NS g-ns-377.awsdns-57.co.uk.
awsdns-57.co.uk. 5 NS g-ns-953.awsdns-57.co.uk.
Authority
The response has no authority records.
Additional
g-ns-377.awsdns-57.co.uk. 5 A 205.251.193.121
g-ns-953.awsdns-57.co.uk. 5 A 205.251.195.185
g-ns-1532.awsdns-57.co.uk. 5 A 205.251.197.252
g-ns-1853.awsdns-57.co.uk. 5 A 205.251.199.61
g-ns-377.awsdns-57.co.uk. 5 AAAA 2600:9000:5301:7900:0:0:0:1
g-ns-953.awsdns-57.co.uk. 5 AAAA 2600:9000:5303:b900:0:0:0:1
g-ns-1532.awsdns-57.co.uk. 5 AAAA 2600:9000:5305:fc00:0:0:0:1
g-ns-1853.awsdns-57.co.uk. 5 AAAA 2600:9000:5307:3d00:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0