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this thread which discussed similar problems recently, however I do not think the same cause is to blame this time.
What appears to be happening at the moment is that the DNS responsibility for the e4education.co.uk domain (which
www.tudorhallschool.com is an alias to records of) appears to be being migrated from Rackspace to LiveDNS (perhaps as part of a general hosting move) however it is being done badly because inconsistencies of authoritative data are occurring and cracks appearing. In particular, both Rackspace and LiveDNS both consider themselves authoritive for the e4education.co.uk domain but only Rackspace have any records within it (e.g. web7.e4education.com in this case). Unfortunately Nominet (.uk) say that LiveDNS are the authority...
The bottom line of both these episodes is that whoever is responsible for DNS for UK schools really doesn't know what they're doing. There's really no excuse other than incompetence to account for what is happening here. I don't mean to sound nasty, but given the consequences of getting this wrong it really ought to be being managed by someone with a handle on what needs to be done.
In your particular case I don't think there is much that Plusnet can do about it because their resolvers are only taking the word of the broken authotitative servers (moving from PowerDNS to BIND might help but that's only because it behaves differently when looking up CNAMEs (aliases) - neither is fundamentally right/wrong though). The likes of OpenDNS are a bit more resilient to these problems through extreme caching of previous results, and perhaps they're not using PowerDNS either.
Mathew
