I’m an accountant, but it’s a while since I was doing company car and van tax, but here is how I see it.
You are basically paying the lease, but the company deducts it from your salary before tax.
The car isn’t a company car. So that section does not need completing.
BUT… and it’s a big but.
HMRC don’t approve salary sacrifice to lease a car. It’s OK on rail tickets, bikes and child care. Not on leasing cars.
The BIK is the saving on tax/NI you won’t be paying.
It put’s you in a bit of a weird position. The car lease should be deducted after tax.
I’d have a word with payroll/HR first, but you’ll be liable for tax on the difference between the tax/NI saved – it’s still cheaper though. It’s just messy for you. The BIK will be on that 30-odd percent or more of saved tax/NI, which is about a third of that saved.
So, you save £1000 year on the deduction, so it might cost you an extra £300-£400 in tax. So net saving is £600-£700. It’s just messy filling in the returns – very messy – this is where you need advice, as I’ve never seen this.