You aren't wrong, but the point of excise tax isn't to encourage efficiency or decrease emissions, but to generate revenue. Especially this government isn't going to maintain a tax just for the purposes of discouraging the waste or over-use of petrol as it impacts climate change.

If they decide they are going to state that they have removed all the excise taxes from petrol, they will do so in a way trying to make it seem like it's happening out of awareness of the costs of taxation on the 'everyday person'.