Hi Bedlam
I had one of these with a 20 yr term, matching my mortgage term. I cashed it out in 1998, 8 years early. I received an offer from Scottish Provident which I bettered by selling it to a broker. I wish I'd kept it til 2006 but I needed the money in 1998/9. I can PM you the broker's name if you want. He was dead on and straight up.
You will not get the terminal bonus but a valuation at time of encashment. Whoever the broker sells it to gets the full value at maturity.
Slim