I have pasted this from another forum site. Hope it helps.
"Guidance has been published by HM Courts regarding the issue of claims under s.214 of the Housing Act 2004 for the 3x deposit 'penalty'. Apparently the civil procedure rules are soon to be amended to state that all claims must be started using Part 8 procedure. this blog post explains a bit more. Claims will be automatically allocated to multi track (not small claims) which means that legal costs are recoverable irrespective of the size of the claim. (Obviously, the court might then re-allocate if there were good reasons). This means that tenants will have to be very sure of their case before claiming. This is probably to reduce the number of speculative claims relating to minor technical non-compliance (such as providing details a week late) as well as 'revenge' claims."
Bearing the above in mind, you might like to seriously consider whether you would win, since the deposit has actually been returned to you. In these cases, because the legislation is very badly drafted, it is open to ambiguity and it seems to depend on which judge you get as to whether you win or lose.
If you lose, you might be liable for costs.
I was not around for your original postings so do not know the background, but suggest you think carefully, or maybe take some legal advice, before proceeding.