Not to go off topic strawberryfields, but what's wrong with the OP claiming incapacity benefit and having life savings? If, for example, they had savings before initiating their claim then why would he/she not be entitled to the benefit? That would suggest that an individual who squandered their income could have the benefit, but someone who saved some of their money could not? Think about that, I don't think you'll find that fair.
Squidge - you've got your answer in terms of what you can do to get this money back. I have to say though that morally at least, if this person was indeed an old friend I would let it go. Indeed, living on the sliver of every last penny cannot be an easy thing. On the other hand 70% of the loan has been paid back and as stated, many people do not keep to their word and pay back loans from friends and relatives.