My brother is a paid singer pianist in a posh hotel in Orlando. I don't know how much he is paid, but I know he really relies on the tips he gets. I also know that when tourism fell after Spetember 11 2001 the hotel cut down his perfroming nights per week.

He also has stiff competition from New Orleans musicians who have settled in Orlando after Katrina. I guess in the credit crunch will make things even worse.

In the US it is expected that there will be a receptacle for gratuities and it is very easy to put a few dollars into a jar or hat.
But how to manage it in the UK without insulting the musician who isn't advertising in such a way?

I think a tip jar or hat at least makes it clear that gratuities are gratefully accepted.

There was a time that my brother took the edge off his tip jar (a giant brandy snifter) by wrapping a teddy bear around it and putting some little sign like Money for my honey, or some such.

In the UK, roaming folkies, need to pay for petrol or public transit and accommodation expenses and food. Would it be so terrible for them to set up say a VW campervan bank on table with note, "Help me get home?"

It would encourage me to donate to UK musicians who made the effort to come a distance to perform. I mean, really do they make that much even if they are a paid guest? I don't think so.