Complex sentence: Comprehensive redevelopment of many British town centres occurred in the 1960s and 1970s, which often resulted in development of larger store formats, often with modernist styles of architecture significantly different from their surroundings.
Split into simpler sentences: Comprehensive redevelopment of many British town centres occurred in the 1960s and 1970s. This often resulted in development of larger store formats, often with modernist styles of architecture which significantly differed to their surroundings.