I don't understand Saswitch fees. I was reading an article on the Sunday Times website, which I was led to by this blog post.

I was about to post a comment saying how, if the banks won't all drop their fees, then changing the way the fee is charged will introduce more competition. When I tried to elucidate this I ended up going in circles trying to figure out who pays who what when.

How do Saswitch fees currently work? If I am a customer at Bank A and draw money from a Bank B ATM, then who pays whom the Saswitch fee (which eventually comes out of my pocket)?