Company fuel card

• My employer provides me with a taxable cash car allowance and use of a Co fuel card.
• I use the fuel card to purchase both business & private fuel
• At point of purchase I make it clear that I’m purchasing all the fuel on behalf of my employer.
• From the total fuel spend my employer deducts business mileage at the rate of 45p &25p

Questions

• Where after the above does the excess private fuel spend get declared on my form P11D, box c, e ,m or even n
• Any NIC liability on the taxable amount? If so Class 1 employer & employees, or class 1A
• Can the 45p be applied to the whole spend for NIC purposes

Thanks