Devon does not have the authority to pass by-laws which trump national legislation, jake, so your analogy is specious.
However, the idea that the Tobin tax will be used to fund future bail-outs is somewhat misleading. When he initially presented his plan the president of the European Commission Jose Barroso officially presented a plan to create a new financial transactions tax "to make the financial sector pay its fair share". Its “fair share” of what was not discussed but I cannot find any reference to a fund being set up for future bail-outs. In any case, the UK already makes a levy of 0.5% on share transactions so it could be said that the financial sector (or at least its customers) is already making a substantial contribution towards its “fair share” (whatever that may be). The closest I can get to confirming that the tax will be used as suggested is a BBC report which says “It is not yet clear how the proceeds of the tax will be used, but one possibility is that they will be collected by the European Commission to finance a bailout fund for eurozone banks.” I imagine there are plenty of other “possibilities”.
This tax will do nothing to govern or regulate free trade - especially not financial transactions. There is not a cat in hell’s chance of it being adopted globally and all that will happen is that traders will shift their business to places where it is not imposed making the EU countries that are intent on implementing it even less competitive - just what they need at the moment.
The EU should resist the temptation to try to impose harmonious fiscal conditions across the continent. It has shown that it is singularly inept in such matters as is adequately demonstrated by its crowning achievement that is the single currency. Look what a roaring success that turned out to be.