Re: Ppi
My take on this.
If you went with one of these fly-by-night PPI companies then firstly that was ill-advised imo and secondly you will have signed a form giving them the various rights, such as the right to dig into your finance details, access your credit stuff and so on. There will doubtless be a clause in there about how much of the proceeds they are able to take for themselves on any mis-sold PPI uncovered.
You need to read through that document very carefully imo. Post a copy up here if you would like others to comment on it.
I would tend to treat this a bit like job agencies. If you go to an agency and sign up with them to find a job for you, then in doing so, you are contracting with them and they are then entitled usually to some percentage of your initial wage. If, whilst they are looking for you, you discover a job yourself then the outcome depends on whether that job agency is attached to or linked with the company employer you found. If they are, then even if you go direct to that employer you will still be liable to pay the agency.
I suspect PPI will be similar. Once you contract with a company to do the investigative work, then doing it yourself is a bit of a grey area