Your friend would then still have a debt of £8.500 regardless of how many cards it is spread over.
His best bet would be to apply for another credit card, that has 0% interest rate over the maximum amount of months available.. Do a balance transfer of £8.500 onto the new card with a one off balance transfer fee to pay .. often between 2-3%.
Under no circumstances can he use the new card to make any purchases. This card is purely a vehicle to make sure that every penny he pays back actually goes towards reducing the debt.
In recent years I had to bail someone out to the tune of £7.5K .
I applied for the card in my name as their credit rating was shot.
The transfer fee was approx £210 and they had 31 months to clear the debt. Whereas prior to that they had been paying approx £160pm interest to the card issuer. So only about £40 of their £200 monthly re-payment was going towards the debt, the rest was interest.
Now with the new card, it was the full £200 going towards the debt. It doesn't take much working out.
https://www.moneysavingexpert.com/credit-cards/balance-transfer-credit-cards/