Very astutely observed, if I do say so myself. It hardly helps your case, though, does it?
OK, say I buy your insurance for £30 a month, and at the end of 300 months I get my £9000 back. But I can get the same cover elsewhere for £10 a month, so suppose I take that, and invest the difference at 5.17%. After 300 months, I've doubled my £20pm, so I have £12000. I think I like that better than £9000.
That's probably what your company does anyway. It uses 1/3 of the premium to underwrite the insurance costs, and pools the rest into lucrative investments with returns sufficient to (say) triple the money. Now your company has lost £3k of my £9k on underwriting, but has turned my £6k into £18k, of which it gives me "my £9k back" and keeps the other £9k. Nice idea. Investing OPM is always a good idea. But what about me when your company's investments crash in year 24?