So - you want to swim across the English Channel...

One way to start is by contacting the the Official Channel Swimming Association. They track all properly authenticated swim attempts since 1875 to the present day. They may not be the only ones, but they do have quite a history behind them. Since 1927, Cross-Channel Swims have been organised and regulated by the Channel Swimming Association itself and all swims officially observed by its designated Officials are faithfully recorded.