A differential in the rate of excise applied to petrol and that applied to diesel exists due to diesel being the traditional fuel of business. Commercial vehicles such as heavy goods vehicles had no economically viable alternative and the reduced excise rate on diesel was applied in recognition of this and the role of transport in the wider economy where added fuel costs could ultimately translate into added retail prices.
Nonetheless I am aware that a balance must be struck between the different policy objectives, which of course include environmental objectives. When I am considering the appropriate excise rates applying to auto-fuels in advance of Budget 2019 I will consider all of the elements involved, including the environmental rationale of applying excise duty on auto-fuels.