Nigel,
I don't see it as double discounting, rather 2 stages of discounting:
Stage 1: Financially adjusting for "future value" :
1) Inflation (£1 today being worth more than £1 in future)
2) Chances of survival
But it doesn't account for the fact a pension is tied up for 25 years. Severely limiting its real "value" to the individual. Quite simply - you cannot spend it.
So you need...
Stage 2: Determining the individuals immediate need for cash today.
To me personally £1 CETV is worth much less than £1 cash.
- I can spend cash on immediate needs such as a house deposit.
- I can use cash to pay off debts that are on 17% interest rates far higher than 5% pa. My 25K debt could cost me 50K eventually to pay off. Would be so much better to have the cash now to pay it off in full.
- I can invest cash in a high growth (perhaps internet

) business
If I am prepared to sell my pension for 80k (and by the way if anyone knows if there is a way I can do this - please let me know) then it isnt worth its 150K to me whatever the CETV says.
Another way to view this is to bypass the whole future discounting thing.
Imagine if you were offered 150K cash or 150K in a building society account paying 5% that you could not access until you were 65.
They just aren't equivalent.
=> The 150K cash offers freedom, options, choices - now - today.
=> The 150K tied up in the building society account offers some security of a comfortable old age.