UK regulators have branded firms involved in mergers and acquisitions "complacent" and challenged them to do more to prevent information leaks, after a review into the problem unearthed nearly 200 insiders on a deal at just one company.

The revelation was contained today in the results of a review by the Financial Services Authority, the UK's financial market regulator, of the safeguards in place to prevent the leak of inside information during M&A deals, after a previous study found that market-sensitive details were divulged ahead of one in three takeover announcements in 2004.