By Jack Mendel A “major operation” by the financial watchdog and national crime body has arrested three men accused of insider dealing and money laundering linked to gangs. The Financial Conduct Authority (FCA) and National Crime Agency (NCA) said it conducted an operation earlier in the month in which three London-based men were held. The three were detained on suspicion of insider dealing, conspiracy to insider deal and money laundering linked to organised crime. Today the FCA announced a fourth was investigated under caution. The arrests were made on 1 February according to the FCA, with th…