Apex domains cannot have CNAME records.
Question and response
Question
dig gw2.uk. NS
Answer
gw2.uk. 2 NS a.gw4.uk.
gw2.uk. 2 NS a.gw8.uk.
gw2.uk. 2 NS a.gw2.uk.
Authority
The response has no authority records.
Additional
a.gw2.uk. 2 A 193.200.99.172
a.gw4.uk. 2 A 185.53.45.23
a.gw8.uk. 2 A 91.123.227.101
a.gw4.uk. 2 AAAA 2a0a:bb00:0:0:0:0:0:17
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0