Last of the Summer Wine : Tom

As a longtime fan of LOTSW 1972-99, could anyone clue me in as to why Tom Owen was chosen to "replace" his father on Bill Owen's death? -- not as the same character, but taking almost as big a role as his father. Compo as played by Bill Owen was a uniquely eccentric good-time-Charley and independent spirit, whereas Tom Owen played Compo's son as a smarmy people-pleaser -- completely upsetting the balance of the show. Was Tom a mate of Roy Clarke's, or just happened to be on hand?

I imagine someone thought it would be a nice touch to bring him in after his father's death. However, he had not had much of an acting career before that and he had a very distant and troubled relationship with his father. He also didn't like Kathy staff, who, he claims, bad-mouthed him to other cast members. The interview below from 2010 is very revealing.

http://www.dailymail.co.uk/femail/article-1295547/Son-Compo-Dad-arms-says-Tom-Owen-veteran-star-Last-Of-The-Summer-Wine.html