uk.mdsl.com has no CNAME records.
Question and response
Question
dig uk.mdsl.com. NS
Answer
The response has no answer records.
Authority
mdsl.com. 5380 SOA ns-603.awsdns-11.net. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0