Cycling while on the phone

Driving from Runcton to Sidlesham today, Wednesday July 10, I observed a teenaged schoolboy (in uniform) cycling ahead of me, just past Hunston village, at about 4.35pm. Neither of his hands was on the handlebars, and his head was bent over his mobile phone, on which he was texting. He was not wearing a helmet, and was cycling erratically, with his eyes more on his phone than on the road.

As soon as it was safe to do so, I overtook him extremely carefully, but if he had swerved in front of my car and hit it, I wonder whose fault would it have been? M CAMERON (MRS) Chalk Lane, Sidlesham