I've heard a lot of talk about hybrid vehicles which switch to electric
power in places like high streets where fumes are a big problem

Indeed, I spent a sunny summers day in Manchester last year, lovely
place, with no stinking buses arround the area. It was all
pedestrianised apart from the metro. Down south "pedestrianised" seems
to mean chocked with buses beltching diesel fumes making it impossible
to breathe. I don't notice fumes from cars, even 4x4s, but buses are
worse than smokers.