I done it about 5 year ago by just filling in a form and sending it to RBS.
From a loan and a credit card I had when I was 18 which was an overall borrow of 3.5k I got over 1.5k back, which I didnt understand how it was so much but was delighted.
I seem to recall the paper had a question worded around were you told about PPI or had it explained (Something like that) and I put down it was explained to me and that I had to take it in case I was ever unemployed it would give me some sort of relief for a few months of the payments.
This scenario did happen in that I was in a job and basically was told by HR I could hand my notice in, or go through a process I would most likely get the sack from. Of course I handed my notice in an left with a nice clean record, but PPI didnt cover me as I had left voluntary. I explained it was not sold to me like that and I guess that was reasonable enough reasons for them to pay out. Or I just got lucky at a time when they were just paying out, but they might be vetting it a bit more now.
I got about £5500 back from RBS a few years back for loans I took out with Lombard Direct. I only had information about one and only expected to get any money back from that, but RBS sent me cheques for 3 separate loans. I just sent it in myself using templates I found online.
I tried a couple of them but got told I had no PPI. I did credit card applications online, even back in early 2000s so I suspect I just opted out of any Ďextrasí at that point. Donít recall anyone trying to sell it to me tbh.
Do know a couple of people who got 4 figure pay outs recently though.