yea...no.
Get your money back, tell him to get a grip on himself, and tell him that if it were a lending company he'd be dealing with, he'd be fucked.
And next time, PLEASE! For the love of whatever's still good on this planet, write down any loans on paper, and if it's a big sum of cash (50 pounds upwards), make a payback deal so that they pay you in installments per week (say 10 pounds a week), and if them miss one, they better be ready whenever you need a tenner to lend you one.
My sister did this when she bought a Macbook: borrowed from my dad, payed back 300 dollars a month over 3 months to get even. Well, except with a that amount of cash, she did the right thing to not miss her payments, obviously.
That reminds me, you can get him to not repay it, but instead let you borrow the money he owes you from him whenever you need it. After all, he won't cough up 8 pounds right away when it's debt, but he probably wouldn't mind lending a pound or two every so or so days if you go out and do something. I did this when a friend refused to pay me back 10 pounds, and I easily made all my money back this way with less hassles than constantly reminding him.