It is illegal for someone to keep someone elses property to with what they will. Essentially this is a Criminal Offience pertaining to The Theft Act.
Your Rent Arrears and Deposit are a civil matter.
Frankly, as a Landlady, I wish that ALL my Tenants would remove their furniture prior to leaving my properties. I am left many a time having to get vans etc to take stuff away (good stuff at that) to the tip. Which is costly - on me.
If the flat was damp (not condensated) then your Landlord would have been legally obligated under The Landlord and Tenants Act to rectify this matter, however, this would not have given you a civil legal right not to pay your rent.
I am interested to know if you were in receipt of any HB? If so, how did you manage to get into arrears ?
Hope your move goes well.
katie. x