Arokh,
To be honest, I think if you allow this to fester I think it will end up hurting you a lot more than anyone else.
You have been badly treated, no question, but your next stop should be the Citizen's Advice Bureau if you wish to push for redress, as you need to know exactly what your rights are under law and how you can go about claiming them.
Reporting a firm for software piracy when you THINK they MIGHT be guilty is not a good move. After all, unless you are certain the possibility exists that you may be wrong. What then? Your ex-boss could rightly say you are a disgruntled employee looking to create trouble for the company which may land you in trouble rather than him.
Rather than revenge schemes - however justified - you are far better off finding out what options are legally available to you, then, when you have pursued them, chalking the whole thing up as a bad experience and moving on with your life.
