Hello,
We've fixed the nameserver issue at Nominet.
If you aren't on our TAG then please could set your nameservers back to ns1.krystal.co.uk and ns2.krystal.co.uk at your earliest convenience.
(The ONLY way that we could rescue our original ns1 and ns2 nameservers was to move the current ones on to new nameservers - we picked ns5 and ns6 as they weren't in use)
ns5 and ns6 have the same glue records so your domains will work absolutely fine but it'd naturally be better to have your nameservers set back to our standard ones.
There'll be an email later with a longer explanation but for now, thanks for your patience and understanding, and apologies for inconvenience caused.