International agreement would be great, but it's not vital. In Europe, countries are negotiating to reach consensus on introducing an FTT. But in the meantime, individual countries can act alone.
The IMF has clearly stated that FTTs exist in all the major financial centres already, without driving business away. The best example of this is the UK, where we have a stamp duty of 0.5% on all share transactions. The UK’s major competitors do not have this and there certainly is no global agreement, yet it is a successful FTT that raises around £3 billion each year. It is designed so it can’t be avoided and London remains one of the biggest stock markets in the world.