Complex sentence: The main characters are six core characters were devised to be "regular people, not distinguished by their careers or by crime" and were based on people from Mike Bullen's life, along with characters who became integral to the programme as Cold Feet progressed.
Split into simpler sentences: The main characters are six core characters were devised to be "regular people, not distinguished by their careers or by crime" and were based on people from Mike Bullen's life. Along with characters who became integral to the programme as Cold Feet progressed.