if the account which the overdraft is against is a joint account your husband must include this, as he must all non priority debts, in his bankruptcy and by doing so he is no longer liable.
The problem is that as it is a joint account you as the now singular account holder are liable for the full £5000. He cannot pay off this overdraft pre bankruptcy as this may be classed as preferential treatment by your husband for the benefit of one creditor over the rest. But you can pay it off as you are not declaring bankruptcy.