Yesteray i had 20 pounds, I waited for the bus 40 minutes it was freezing! I jumped in and i gave him 20 pounds and he said i couldnt travel because he didnt have money change. luckly there was a friend of mine behind who did. However it happned to me that some other times...and the bus driver didnt seem to care. He said ok dont worry...So what is the rule here in london?