People who work in banking get big bonuses because they work in the money industry.
Similarly people who used to work in coal mines came home from work covered in coal dust.
Nurses in A&E (and doctors for that matter) don't earn similar bonuses because there isn't a lot of money swilling around A&E on a Saturday night.
As a lawyer, you will find it easier to pick up a bit of money if you facilitate a large business deal or a multi-million pound divorce than if your clients have no money what so ever.
I think the Robin Hood Tax is a non-starter because, as has been pointed out, the banking industry doesn't have to do business here at all. You might as well have a tax on hopping to work. It would only work if the banking industry wanted to take it on as some kind of PR thing.
Plan B could be where we put chewing gum on the seats in reception because that would be really annoying.