Apex domains cannot have CNAME records.
Question and response
Question
dig districtb.co.uk. NS
Answer
districtb.co.uk. 5 NS ns2.districtb.co.uk.
districtb.co.uk. 5 NS ns1.districtb.co.uk.
Authority
The response has no authority records.
Additional
ns1.districtb.co.uk. 5 A 194.164.92.177
ns2.districtb.co.uk. 5 AAAA 2a0a:6044:acd0:0:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0