The benefit on vehicle(hired or operating lease) given to an employee for the purpose of exclusively use in private

"The value of benefit to an employee from the (fully or partly) private use of any motor vehicle should be the market value"

If the company pays hiring charges or opertaing lease rentals on a vehicle which has been given to an employee exclusively for his private purpose ,the market value of the benefit will be the amount of rent or hire charges paid.

Therefore when ariving at the PAYE liable employment income ,the amount of hire charge or rent should be added to the employment income since the market value is ascertainable.