Apex domains cannot have CNAME records.
Question and response
Question
dig venuetoolbox.co.uk. NS
Answer
venuetoolbox.co.uk. 4 NS ns1090.ui-dns.biz.
venuetoolbox.co.uk. 4 NS ns1090.ui-dns.com.
venuetoolbox.co.uk. 4 NS ns1090.ui-dns.org.
venuetoolbox.co.uk. 4 NS ns1090.ui-dns.de.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0