Apex domains cannot have CNAME records.
Question and response
Question
dig rbs-ema.co.uk. NS
Answer
rbs-ema.co.uk. 5 NS udns2.cscdns.uk.
rbs-ema.co.uk. 5 NS udns1.cscdns.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0