You are entitled to claim back from him up to 3 times the deposit through the County Court as he failed to protect the deposit in a recognised scheme.. The relevant statutory provision is section 213-214 Housing Act 2004. If the tenancy has ever been renewed, that is a further breach and you are entitled to the same for each breach. On top of that you are entitled to the return of the deposit you do remain liable for any damage to the property but not from the deposit.
There are many solicitors now dealing with this on a no win no fee basis so it would be worthwhile making a few telephone calls.
Can I clarify anything for you? Please rate the service positive so that I get paid. We can still exchange emails. Best wishes. FES.