Banks everywhere are muscling in on foreign exchange - just as the costs of building a forex business are rising and spreads are tightening. Europe's commercial banks are trying to replace business lost with the onset of Emu. US investment banks are bolting forex on to their core activities. They can't all be winners. But, as Antony Currie reports, they can make life harder for those already at the top. Euromoney's 20th annual foreign-exchange poll follows. Research by Rebecca Dobson.