I managed to dig out the paperwork and it was detailed on there, forming part of the repayments. Although both loans were a long time ago, I don't remember the insurance ever been offered as optional, it was just included as standard.
I think it really varies from company to company. I've made two claims, sending identical letters to each of them. The first lot, Citi Financial, made me complete a lengthy questionnaire before taking forever to finally issue a cheque (after I'd got on to the ombudsman). Santander on the other...
DON'T use a third party company, they'll fleece you for at least 10% of any claim as well as take forever. Write a letter yourself, something like this:
Re account number:
Dear Sir/Madam
After having consulted a financial advisor, I wish to make a claim for mis-sold Payment Protection...