Complex sentence: OLs have always played an important part in the life of the town of Rugby, including in the' 50s mounting very successful amateur dramatic productions which were part of the momentum that led to the establishment of Rugby Theatre.
Split into simpler sentences: OLs have always played an important part in the life of the town of Rugby. In the 1950s, they mounted very successful amateur dramatic productions which were part of the momentum that led to the establishment of Rugby Theatre.