I doubt if a loan of any sort for £2000 is wise, if he needs £800. Do you believe he will pay off his debt? If not, a loan would just land him in deeper sh*t than he is in: unable to pay £400 to get his car fixed - did he not reserve money over last months. How much does he earn, if working at all? Do not tell him but perhaps you should write-off your £400 unless he has made any repayment of your loan. He needs to be taught, as young as possible that we all have to live within our means. Best to be "cruel" to be kind and leave him to his own devices. Do not be emotionally blackmailed. I have never "lent" money to a relative or friend (it destroys relationshps). If I knew they were sensible over money management and were surpringly desperate for money I might consider lending/giving them money provided I could EASILY afford to do it.
Has your brother anything to sell or does he think he deserves all luxuries that everyoneone else has? Luxuries are anything more than a roof over your head, food, water, table and chairs, radio or cheap TV. They do not include computer, Sky TV, high-cost mobile phone, games machines etc.
MY BROTHER SLOWLY BLED MY MOTHER WHITE, DRIP-BY-DRIP OVER DECADES and I had to help her out with items he could not access.
Good luck to you & your brother xxx.