Apex domains cannot have CNAME records.
Question and response
Question
dig healtheweb.co.uk. NS
Answer
healtheweb.co.uk. 1 NS ruth.ns.cloudflare.com.
healtheweb.co.uk. 1 NS seth.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0