One – but only one – of the challenges to the bedroom tax is the minimum size of your smallest bedroom.
Many of the smallest rooms in social housing are less than 70 sq/ft and thus a boxroom rather than a bedroom.
A single bedroom has to be 70 sq/ft or 6.5 sq/m to be classed as a full (1.0) bedroom. If it is 9ft x 7ft then it is 63 sq/ft and just 0.9 of a bedroom.
The size standards are found in the 1985 Housing Act section 326 (and see here for an overview http://www3.westminster.gov.uk/docstores/publications_store/overcrowding%20excerpt.pdf ) which ironically deal with overcrowding and set out the 70 sq/ft issue and also the fact that anything under 50 sq/ft (eg 7ft by 7ft) cannot be deemed as a bedroom at all.
If you have a room which is under these requirements then it cannot be classed as a bedroom and you can legally challenge any under-occupancy judgement that says it is a bedroom.
Again, this is only one way to potentially combat the bedroom tax: the State has a shitty habit of closing down any loopholes that spring-up in its face, as evidenced in a recent workfare ruling.
We argue that it's only tenant solidarity and direct action that will see the working class get the goods.
But, it is worth measuring up your smallest room to see if they are classed as a full bedroom or not.
If you want to read an accessible legal view of this try here - http://nearlylegal.co.uk/blog/
2013/02/room-without-review- thoughts-on-tackling-the- bedroom-tax/
Thanks to @speyejoe for details.