Yes. What the middle man will do is ask you for a list of banks, loans and credit cards you've had dealings with. Then they'll send each organisation a request, on your behalf, for the information it holds about you. That's how they identify whether or not you had any PPI. You can do this yourself. The request to the organisation is called a 'subject access request', it is made via your rights under the Data Protection Act. Each request costs a tenner, and they have to give you what they hold within 40 calendar days (just under 6 weeks). Then you sift through it and see if you've been making any PPI payments, or signed any deals which included PPI in the small print.
After 10 years of lurking, I only registered to correct this.
A DPA request is the 2nd step of the process.
The first step is simply to download and complete the PPI Complaints form for each of the Financial Institutions you're querying. The forms take 10-15 mins each, and it costs the price of a stamp to post. If you don't know you account numbers with those institutions, you can say so on the forms. Your D-O-B, address and previous addresses will be used to uniquely identify you.
The DPA request is only required, if they respond and state that they cannot find you in their records, and you believe to the contrary.
I've just completed the first step with by Bank, and the Building Society with whom I had my mortgage.
My Bank has refunded £300 in PPI it applied to my current account at some point in the past; my previous Building Society has acknowledged my claim, acknowledged that PPI was in existence, and communicated that my claim will be resolved in eight weeks.
This has cost approx. 30 mins of my time, and two first class stamps.
The easiest way to find the PPI complaints form for any organisation is Google; just ignore the third-parties that appear at the top of the search results, and choose the result that has the URL of the organisation you're querying.