BIK tax is very different to vehicle tax here in the UK and additional. With EV’s though they are exempt from annual road tax at the moment because they do not produce CO2 emissions. You still have to tax the car, but it’s £0. BIK is calculated by the value of the car, your salary banding and the amount of emissions it produces. EV’s are very cheap as they don’t produce the latter however. This tax exists because it’s a perk and deductible from a persons salary. Having servicing and tyres, repairs etc included is also factored in.
For example if someone was to go for a BMW 520D, the tax would be much higher as it produces emissions and you’d be liable additionally for an annual vehicle tax based on this, plus it would have an additional £355 annual premium as the car is valued over £40k. Confusing, but it means at the moment EV’s are very cheap company cars and my wife pays £20 a month in tax, doesn’t have to pay for maintaining it and 90% of our charging is free.