Apex domains cannot have CNAME records.
Question and response
Question
dig unitedhosting.co.uk. NS
Answer
unitedhosting.co.uk. 5 NS ns2.unitedhosting.co.uk.
unitedhosting.co.uk. 5 NS ns1.unitedhosting.co.uk.
unitedhosting.co.uk. 5 NS ns3.unitedhosting.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0