Why are electric motorcycles not required to pay the parking tax like other motorcyclists?

If Westminster council states that the motorcycle parking is not based on emission levels, then why are electric motorcycles exempt from the parking tax on the basis that they take the same amount of parking space?

The reason electric motorcycles are allocated free parking is because the City Council wanted to address the greener issue, regardless of how much space a vehicle uses. Westminster is one of the worst air pollution hotspots in the UK with around 80% of particulates coming from road traffic. Due to this a decision by the Council was made to consider a system of differential charging based on emission levels. Electric vehicles park for free because they produce zero tailpipe emissions. As a result, they do not contribute the high levels of air pollution we have in central London.

Westminster's decision to introduce a charge for motorcycles as stated was not based on environmental or congestion related concerns, but to address the ever-increasing demand for Westminster's limited kerbside space and due to the reason above electric motorcycles were exempted.