uk.mdsl.com has no NS records.
NS records for this zone are defined at mdsl.com.
NS records for this zone are defined at mdsl.com.
Question and response
Question
dig uk.mdsl.com. NS
Answer
The response has no answer records.
Authority
mdsl.com. 86400 SOA ns-603.awsdns-11.net. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0