Taxation with a company car and new job?

Update: So I'm starting a new job where i'll be given a company car and fuel card. The company policy says they will pay for all fuel on a provided fuel card, but that which i don't log as "business miles" will be deducted from my salary and taken as "personal miles". I'm currently in... show more So I'm starting a new job where i'll be given a company car and fuel card. The company policy says they will pay for all fuel on a provided fuel card, but that which i don't log as "business miles" will be deducted from my salary and taken as "personal miles".

I'm currently in 20% UK tax bracket, but read that the P11D value is added to your salary? If so, it's likely I'd just be into the 40% tax bracket. Does that mean i'll pay 40% tax on my monthly income or just charged at 40% for BiK tax?
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