Here's some examples of a Peugeot 308 estate on my scheme. The top two are a 1.5 diesel and a 1.2 petrol (hardly setting the world alight are they) and the bottom one is the EV.
£300 per month in BIK WTF!
Because the system now is there to incentivise you to pick an electric car. This is the point. They do not want you picking a diesel or a petrol car, so the tax rates on these have been steadily increasing for years.
This is always how its worked - its always been there to encourage people to select lower emissions cars. It's not a surprise that higher emission cars are made expensive on such schemes - this is to discourage people from selecting them. All that has changed over time is what is considered to be a high emission car. Years ago it was cars with large engines, now its cars with basically all engines.
However what I am saying is it's not a company car from my perspective, because I don't get a car allowance or car as part of my package.
It doesn't matter what your perspective is.
So if I get a car through the scheme, I'm paying for it (through a salary reduction) not the company.
Ok, so lets look at this from the way you think it should work.
Lets say that the benefit in kind tax is removed from the diesel in the first example.
The cost of the lease is £726 a month - this is what the car is costing your employer. You then have this taken from your salary before tax, meaning you save £305 in tax and national insurance. So now that £726 lease is only costing you £421 a month, before the application of company car tax.
But this is because the government is now losing that £305 a month in revenue from you. Why? Who should pay for that? What is the point in giving you a £300 a month tax saving for driving a diesel Peugeot? Why should anyone but you pay for this?
So, instead what happens is that the reduced tax is effectively made up (sometimes by more than the initial tax saving) for through benefit in kind tax if you select the 'wrong' vehicle. So, if you pick the diesel, there is no saving because nobody but you benefits from it, it may even cost you more.
The government has decided that it is happy to give up tax revenue to encourage people to select zero emissions cars. This is why, therefore, the benefit in kind tax is very low on the electric car. You make a considerable saving, so that when faced with the decision between diesel or electric, you go for an electric car.
As for why the diesels are even offered - why not? They are just orders through a lease company, if the car is available it'll be on the list.