LaBranche, the US specialist trading firm, has lost its fight to avoid turning over thousands of emails to the New York Stock Exchange as part of an investigation into possible trading irregularities.

An NYSE panel has ruled that LaBranche, one of the biggest market makers on the exchange, must hand over an estimated 8,000 emails. The NYSE is expected to impose a censure and having determined that LaBranche failed to co-operate with its investigation.