Replacing a split clear plastic filler tube in a Vernon Tutbury cistern?

My VT cistern has a thin, clear plastic tube which attaches to the ball-cock mechanism which is part of the whole water refill unit. The tube has split at the top and the result is that water always enters and runs through the Cistern into the toliet bowl.

Do I have to replace the whole in-pipe/ball-cock/tube filler mechanism as a unit or can I take out the filler mechanism, buy a tube and just fit that?