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