Soldato
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.
It doesn't matter what your perspective is.
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.
I understand your point but consider it this way.
Job A is offered at 50k. No company car or car allowance.
Another job B is offered at 50k + car or car allowance (let's say nominally worth £5k).
It's right that job B is taxed with BIK for the car, because he is recieving a non salary benefit.
It's not right that job A is taxed BIK for a car because person A, if he has a car, is buying it out of his own pocket.
The whole point of salary sacrifice is to save on tax. Eg with pension relief, or cycle to work, or buying a computer on salary sac. There is no point using the scheme if you don't save anything, in fact it's often dearer than open market prices without the tax saving.
Why would a tax saving be offered on a diesel? It's still consumer spending encouraging growth in the economy, that's why.