The chair of Europe’s top securities watchdog has delivered a fresh call for international regulators to co-operate over reforms to the $650 trillion over-the-counter derivatives market, just weeks after the world's largest rulemaking bodies pledged to tackle the issue of regulatory arbitrage together.

In a letter to the Agricultural Committee of the US House of Representatives yesterday, Steven Maijoor, chair of the European Securities and Markets Authority, said "conflicting, duplicative and inconsistent requirements" under new OTC rules could have "serious consequences for global market liquidity and might even have financial stability consequences".