In italy it's normally by 'commune'. I think Piemonte has an over all law that allows it throughout. If you're polite, the worst that happens is they move you on. Don't bother with Rome. Tuscany and Emilia Romagna are good in my experience but the legality varies from town to town. Ferrara was particularly relaxed about it. The police in Parma appreciate the music and tell you with exquisite politeness to move on while moaning about the stupidity of the rule.

Spain is generally fine in my experience. I think you technically have to get a permit, but no-one bothers and even the council employees and police don't seem sure in most towns. The only exceptions were Santiago de compostella and the area around Malaga/Marbella where they tell you to bugger off and apparently confiscate your instrument if they catch you again.

German towns generally allow it but tend to have rules on when and where you can play. By and large, if you move every hour or so and don't play between noon and four in the afternoon you're fine.

I never had any trouble in Denmark or Sweden. I got the impression busking wasn't allowed, but decent quality music seemed to impress people a lot and the police were fairly relaxed. Mind you I might have just been lucky and I left Stockholm quickly cos the hats were utter shit. Malmo and Lund are good. Helsingor and helsingborg are good as well.