Complex sentence: He returned to the UK to manage Associated British Foods (ABF) which his father had established in 1935 and he had served on its Board of Directors from 1949, taking over as company chairman in 1967.
Split into simpler sentences: He returned to the UK to manage Associated British Foods (ABF), which his father had established in 1935. He served on its Board of Directors from 1949, taking over as company chairman in 1967.