Complex sentence: The 40 Mini Es that participated in the UK trial were kept in use after the trial ended in March 2011, participating in promotional activities and forming part of BMW Group UK's official vehicle fleet for the London 2012 Olympic Games.
Split into simpler sentences: The 40 Mini E that participated in the UK trial have been kept in use after the trial ended in March 2011, participating in promotional activities. These electrics cars will form part of the BMW Group UK's official vehicle fleet for the London 2012 Olympic Games.