The UK's TLD (.uk) is spread across 11 DNS servers, as follows: ns1.nic.uk to ns7.nic.uk, then nsA.nic.uk to nsD.nic.uk. Although very few domains actually use the TLD directly, most use second level domains, most commonly .co.uk.
The second level domain, .co.uk, is balanced accross the same 11 DNS servers as the TLD, .uk. The same configuration is also used for ltd.uk, .me.uk, .net.uk, .nic.uk, .org.uk, .plc.uk, and .sch.uk.
Alternative configurations are used for .ac.uk, using ns0.ja.net to ns4.ja.net, and the following servers: sunic.sunet.se, ns.uu.net, ws-fra1.win-ip.dfn.de and ns1.cs.ucl.ac.uk.
The second level domain .gov.uk uses the same five ja.net DNS servers as ac.uk, and the UCL server, it also uses auth50.ns.de.uu.net, auth00.ns.de.uu.net and ns1.surfnet.nl
The Ministry of defence second level domain mod.uk, uses only three DNS servers. relay.mod.uk, ns1.nic.uk and the DNS server at UCL used for .ac.uk and .gov.uk.
The National Health service second level domain, nhs.uk, is served by two DNS nodes, nsa.nhs.uk and nsb.nhs.uk
The police force second level domain, police.uk, seems unrelated to the other uk domain names, using totally different DNS servers as follows: ns2.psops.net, ns0.cwci.net, chtdns1.cwci.net, ns1.psops.net, and ns1.cwci.net