"PS Never let anyone be an authorised user on your card" - unless it is your missus and she tells you to, of course.
But seriously, it sounds like your friend has a pretty slim chance of getting their money back. The other user (who is 'pig headed') has obviously worked out that he can get away with this by ignoring it.
I can think of two possible ways to get something back :
1) if the other person is a smoker/drinker/regular consumer of anything, you could suggest that every time they buy a packet of cigarettes or a pint or whatever, that they put aside the change. Every week they hand over the change (maybe €10, or whatever) and eventually they get around to paying off some of the debt. It might only be a fraction, but by doing this they accept that they *have* a debt. Eventually, if the financial situation inproves they might be in a position to pay off a bit more. If they are allowed get away with the view that they don't have to repay your friend, then they will *never* pay anything off and they will never recognise the debt.
2) your friend could let other people know the situation and let them put indirect pressure on the other person. This one obviously depends on circumstances, big time. If they are out for a drink with friends, family or colleagues and the other person goes up for a round, they could drop a subtle hint about being owed money to see if anyone else picks up. If they do pick up, youe friend could elaborate a bit and say they haven't so much as paid a penny back. Maybe you have had to change your holiday plans, maybe you can't give someone else a loan because you're a bit short yourself since the other person left you high and dry. It's not as if your friend would be saying (necessarily) anything untrue. If people know the person has defaulted on his debt they in turn will drop subtle hints back to the other person and this may encourage him to *start* paying back. It may also just aggrevate them too, so hence the need to take account of the circumstances.
If your friend gets the other person to accept they have a valid debt it is important to get some form of regular payment schedule. Otherwise he might find that the money just stops coming after a while and it will be back to the start again in terms of getting more of the debt repaid.
z