Average number of miles by a company car is 17,500 in 2018 (source: https://www.racfoundation.org/motoring-faqs/mobility#a25)
Average petrol cost in August 2019: 129.2p (source: https://www.theaa.com/driving-advice/driving-costs/fuel-prices).
A Ford Fiesta, the most popular company car in 2018, achieves 55.4 miles per gallon (source: https://www.parkers.co.uk/ford/fiesta/review/mpg-running-costs/).
4.54609 litres in a gallon = 12.18 miles per litre. 17,500 / 12.18 = 1436.78 litres required to do 17,500 miles. 1436.78 * 129.2 = £1,856.32 total cost
Average cost per mile on a Nissan LEAF is 3.9p (source: https://www.goultralow.com/electric-car-savings/home-charging-calculator/). 17,500 miles * 3.9p = £682.50 cost to charge.