The European Union’s top financial regulator has written to Members of the European Parliament, voicing his concern on the direction of new derivatives trading rules being debated by the region’s policymakers.

A letter from Michel Barnier, the European Commissioner for internal market and services, seen by Financial News, expresses his worries about the way that new rules - which require over-the-counter derivatives to be traded on electronic venues - are evolving in talks among policymakers.