Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-48.co.uk. NS
Answer
awsdns-48.co.uk. 5 NS g-ns-944.awsdns-48.co.uk.
awsdns-48.co.uk. 5 NS g-ns-368.awsdns-48.co.uk.
awsdns-48.co.uk. 5 NS g-ns-1844.awsdns-48.co.uk.
awsdns-48.co.uk. 5 NS g-ns-1523.awsdns-48.co.uk.
Authority
The response has no authority records.
Additional
g-ns-368.awsdns-48.co.uk. 5 A 205.251.193.112
g-ns-944.awsdns-48.co.uk. 5 A 205.251.195.176
g-ns-1523.awsdns-48.co.uk. 5 A 205.251.197.243
g-ns-1844.awsdns-48.co.uk. 5 A 205.251.199.52
g-ns-368.awsdns-48.co.uk. 5 AAAA 2600:9000:5301:7000:0:0:0:1
g-ns-944.awsdns-48.co.uk. 5 AAAA 2600:9000:5303:b000:0:0:0:1
g-ns-1523.awsdns-48.co.uk. 5 AAAA 2600:9000:5305:f300:0:0:0:1
g-ns-1844.awsdns-48.co.uk. 5 AAAA 2600:9000:5307:3400:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0