This isn't necessarily a straight forward situation.
Does the company lease the vehicle and then provide it free of charge to the employee along with a fuel card. For UK tax, it's a benefit in kind. For US tax, it's a taxable benefit.
Who pays the insurance? If the company, is it part of the benefit in kind (and the yearly statement for HMRC purposes reflects that - It's been awhile, is it a P40?). If the employee provides the insurance, then that portion surely isn't taxable by either the UK or US?
Some UK companies provide the vehicle, then lease the vehicle to the employee for a set rate, along with a fuel card, breakdown service, and insurance. The company, in this case, may have an agreement with HMRC that allows that no 'benefit in kind' will exist. These same companies may also provide a contract that specifies the employee, when retired, may still lease a vehicle provided by the company, along with breakdown service and insurance (no fuel card) which also is free from being a 'benefit in kind' for UK tax purposes. US tax? It's a simple lease agreement at a set price, does that make it non-US taxable? If it is at a favourable lease fee does that make a portion of it US taxable?