I have not dealt with this before, but as its a police matter, a good place to start to look is the standard police text book Police Law (formerly Butterworths Police Law, and before that Moriarty’s Police Law..I kid you not.)
Local reference libraries often have it, or your own legal department may have it, but if not, it costs less than £25 from the publishers. Could your council invest in a copy?
http://www.oup.co.uk/isbn/0-19-928405-9?view=lawview
As for the appeal itself, there are a number of issues:
1) The amount of and recoverability of the overpayment (appealable)
2) The target for recovery (theoretically appealable but in practice not worth the bother because one of the parties is dead and probably left no estate)
3) Whether or not the LA should recover the overpayment assuming it is recoverable (not appealable)
If I was representing the landlord, I would argue that the failure on the part of the DWP to inform the Council was an official error that caused the overpayment. [Mr Justice Richards held in R(on the application of Sier) v Cambridge CC 28 Feb 2001 QBD that failure to send the NHB8 was an official error, but on the facts of the case it had not caused the overpayment.]
In your case Sier can be distinguished because the claimant could not disclose that his IS ended, nor could he reasonably be expected to realise he was overpaid given that he wont know anything when he is dead.
The landlord can easily argue that he has no duty to disclose anything he does not know and similarly he had no reason to belive he was overpaid at the time he received the payments. The overpayments may well be not recoverable.
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