The current offence of careless driving (undue care and attention) allows prosecution for all of these things already, but it is obviously felt that it needs to be spelled out. Whenever I see a vehicle veering out of lane or drifting between the lines, the majority of the time it’s someone doing something with their mobile phone or lighting a fag (which should also be made illegal whilst driving IMHO).
Worst offenders, I’m sorry to say, are lorry drivers. There’s never a week that goes by that I don’t see an HGV drifting partially into the hard shoulder of the motorway. It’s no wonder that so many people get killed in hard shoulders. The worst example of appalling HGV driving that I saw was one that was veering in and out of the hard shoulder and when I overtook him, expecting to see him on his phone, he had a newspaper placed over the steering wheel!