Apex domains cannot have CNAME records.
Question and response
Question
dig dsl.wavenetuk.net. NS
Answer
dsl.wavenetuk.net. 5 NS dns2.wavenetuk.net.
dsl.wavenetuk.net. 5 NS dns1.wavenetuk.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0