Apex domains cannot have CNAME records.
Question and response
Question
dig threembb.co.uk. NS
Answer
threembb.co.uk. 4 NS dnsxau.ipdesign.info.
threembb.co.uk. 4 NS dnsxau.threembb.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0