If a landlord fails to protect a tenant's deposit (by placing it into a tenancy deposit scheme) it has no effect whatsoever upon the payment of rent. i.e. you can't claim any rent back from the landlord.
However if you'd have applied to a county court during the period of your tenancy, the court would have ordered the landlord to repay three times your deposit. See 'What if your landlord isn’t protecting your deposit?', here:
http://www.direct.gov...ancyDeposit/DG_066373
Since you've not challenged your landlord, through the courts, during the course of the tenancy (and you've presumably been repaid your deposit) I believe that it's unlikely that a court would now entertain any claim from you.
Chris