LONDON—British prosecutors filed criminal charges against three former bank traders for alleged fraud, opening a new front in a global investigation into alleged rigging of benchmark interest rates, with more charges in the pipeline.

The U.K.'s Serious Fraud Office said Monday that it charged three former Barclays PLC traders with conspiracy to defraud for their alleged roles rigging the London interbank offered rate, or Libor. The agency, which opened its criminal investigation in July 2012, also is likely to file charges...