Lib Dems want only ultra low emission vehicles and electric cars from cities . Clegg says he wanted to reduce ' dangerous levels of air pollution ' in cities . Launches awarded 100million ' prize ' for those who build first ultra low emission vehicles .
Lib Dems want only ultra low emission vehicles and electric cars from 2040 . Clegg says he wanted to tackle 'dangerous levels of air pollution ' in cities . Launches £100million 'prize ' for firms who build first ultra low emission car .