My client has an overpayment decision because her temporary accomodation booking ended a week after her new secure tenancy had started.

I'm trying to get any information about the council's duties as a unitary authority (i.e. the HPU should notify the Temporary Accomdoation Team and/or HB department about the new tenancy) that might help.

Alternatively, I would be grateful for any help about where to look for info about whether the landlord should pay the overpayment instead.

You could try and make the above argument, but if I was the LA I'd be countering with something like this:

1) a week is not an unreasonable period in which to act on a change in circs and, therefore, the delay does not constitute an official error (at least 3 CDs would support this argument).

2) although it is the same LA, the relevant departments / sections are not connected in such a way as to make it an official error (probably importing some of the principles in Hinchy & the DWP).

However, a couple of things caught my eye about your post. In particular, your post indicates there was dual liability.

If so, when did the clmt actually move into the "new" property? If at the beginning of the tenancy, could the dual liability have reasonably been avoided? If not, then HB is payable on 2-homes <HBR 7(6)(d)>.

Regards