Apex domains cannot have CNAME records.
Question and response
Question
dig my-tmac.co.uk. NS
Answer
my-tmac.co.uk. 5 NS ns-558.awsdns-05.net.
my-tmac.co.uk. 5 NS ns-343.awsdns-42.com.
my-tmac.co.uk. 5 NS ns-1546.awsdns-01.co.uk.
my-tmac.co.uk. 5 NS ns-1232.awsdns-26.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0