As far as I know despite being a single-use item, these vapes mostly contain rechargable battery cells of type 18650. Even though they are probably rather cheap and low quality cells, they still have around 2300 mAh at 3.6 V current. This gives us 8250 mWh per cell. One million of them would be 8250 kWh, enough for 100-200 electric cars. Every day. In a full year that's 3011250 kWh or around 3 gigawatt hours of storage capacity.
Just pass a law that anything intended to be disposable needs to be made with 100% biodegradable material. Selling refillable oil is obviously cleaner and cheaper to make.
It would need to be naturally biodegradable without leaving any kind of dangerous chemicals. A lot of so called biodegradable plastics can only actually be biodegraded in an industrial compostor.
Smoking yes, the UK has the 2nd lowest rate of smoking in the EU (+UK obviously). There hasnt been any significant anti-vaping campaign I'm aware of, because there is a tension that despite it being bad for you its nowhere near as bad as smoking, so getting people off tobacco and onto vapes is a net benefit. Though there does seem to be a growing consensus that vapes have been too permissively regulated thus far and to righten rules around selling them.