Shares in ICAP had sunk over nine per cent in mid-afternoon trade on Wednesday, making it one of the largest fallers on the FTSE 250.
The group, which is one of the world's largest interdearler brokers, said profit before tax for the six months to September was £86m, down from £139m pounds a year earlier.
In a disappointing trading update, the company cited on-going investment in new businesses, softer trading levels and currency headwinds as the main reasons behind the fall.
The group's full year outlook remained unchanged after it said was unsure whether recent pick-ups in trading for some of its markets would continue.
Michael Spencer, chief executive, said:
Our first half results reflect a market environment that has remained relatively fragile; despite this, we are cautiously optimistic that we have started to see some welcome signs of activity and more positive sentiment returning in recent weeks