Proprietary traders sitting on a profitable trading book would not normally look for a new job in September, with bonus day only months away. But fears that investment banks will this year renege on their implicit bonus promises are prompting even successful traders to seek new employers before the year-end.

Prop traders play the markets using a bank’s capital and are paid formulaically, with bonuses traditionally set at between 12 per cent and 15 per cent of their trading profits. However, bonuses are almost always discretionary and expectations for this year’s payout ratios have plummeted.