How can I earn SOME money at 12 years old?

In 2 weeks, I want to take my friends out for lunch and I agreed to pay. I'm 12 and I need the money urgently, how can I get money? I live in London if that's any help, I don't think it is but just to say, it's not safe to go around the streets to sell stuff or even stay in front of my door since there are foxes around. I was thinking of selling stuff I don't want or even sew something to sell, but I don't know what. BTW, my parents NEVER give me money, since its a complete waste. My Auntie gave me some but its scottish, if you know the restaurant Cosmo's do they accept scottish money??? Please help and HURRY...