Question: which actor has been in the most carry on films?
Answer: Kenneth Williams (26 films, including co-presenting That's Carry On!) played a range of character types, nearly always a lead character. ... 
Joan Sims (24) had the longest uninterrupted run of roles in Carry On films, being in all 20 films (excluding That's Carry On) from Carry On Cleo to Carry On Emmannuelle.