ns-uk.topdns.com has no CNAME records.
Question and response
Question
dig ns-uk.topdns.com. NS
Answer
The response has no answer records.
Authority
topdns.com. 3600 SOA ns-uk.topdns.com. hostmaster.topdns.com. 2026022703 43200 900 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0