The changes you're talking about - both the under-occupancy rules and changes to council tax benefit are both due to proposals by central government to come into affect next April (2013).
Nosda - local authorities have nothing to answer for on this issue - it's all on central government. I'm a housing benefit officer for a local authority and I (and many of my colleagues) are frustrated about rules that have been brought in and are due to be brought in by the coalition government (in fact I've gone back to SH because of the stress the budget cuts have put me under at work). The under-occupancy rules apply to all local authorities and to me they make no sense unless they can re-house people into appropriate alternative accommodation (and with a shortage of social housing I don't see how that's possible).
As for the changes to council tax, council tax benefit is being localised from next April (i.e. local authorities have to come up with and administer their own scheme). However, pensioners have to be protected (meaning if they can't have less benefit because of the changes) but central government are cutting funding by 10% (at least with the authority I work for, not sure if the budget cut is the same across the board). In our authority, 49% of the population of ctb claimants are pensioners - meaning the other 51% will have to have ctb cut to protect the pensioners. The scheme in our authority hasn't been finalised but I can't see anything other than making people pay more towards their council tax.
In practical terms, you need to speak to your housing office. However, I would strongly suggest seeing your local MP and asking how exactly s/he expects you to cope with the changes. It's central government forcing this so they should be made to answer. I also strongly recommend others doing this as well. I've written to my local MP regarding upcoming changes but I think they need to be made to answer to the people actually claiming HB/CTB as well.