Okay there are two books I read as a child and would love to identify.
A) a group of young people are putting on a play/performing at a festival (not sure). Anyway some misfortune strikes. They are stranded at some random town and penniless. They meet a benefactor, who only can lend them enough to get the girls back to London/home. The boys instead stand on a bridge and choose which of two rivers/streams to follow, and the follow it acting at villages to earn their keep. (They don't realise until the end of the Novel that the town was Oxford and I believe they choose to follow the Cherwell rather than the Thames).
B) WWII a young boy escapes; possibly from a concentration camp/ on the way to one, he's possibly been previously in the Warsaw ghetto. He has various adventures, but ends up in Franco's Spain and gets into Portugal.
This is not "I Am David" or "The Silver Sword".