The activist investor waging war with the London Stock Exchange has warned the City institution against undertaking a "character assassination" of outgoing chief executive Xavier Rolet ahead of a key vote on his future.

In a letter to LSE chairman Donald Brydon on Tuesday, Sir Chris Hohn, the head of TCI Fund Management, said Rolet was being "improperly threatened" by the board of the exchange, which he has accused of trying to force out the CEO.