Apex domains cannot have CNAME records.
Question and response
Question
dig dds.co.uk. NS
Answer
dds.co.uk. 4 NS dns04.donovandata.com.
dds.co.uk. 4 NS dns02.mediaocean.com.
dds.co.uk. 4 NS dns05.mediaocean.com.
Authority
The response has no authority records.
Additional
dns02.mediaocean.com. 4 A 168.238.194.53
dns04.donovandata.com. 4 A 168.238.66.105
dns05.mediaocean.com. 4 A 52.71.167.236
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0