There's a brief guide to tenancy deposits in the UK here http://www.adviceguide.org.uk/england/housing_e/housing_fact_sheets.htm. I've rarely had money taken out of my deposit for cleaning/damage (I do a pretty thorough clean before I leave a house) and when I have it was never as much as that. I'd check the details about cleaning in your tenancy agreement. How easy it will be to challenge it may depend whether your deposit was held in a deposit protection scheme but I've never really looked into it.