From 6 April 2016 PAYE legislation is changing. If you intend or already payroll benefits and expenses you must register them with HMRC using the online Payrolling Benefits in Kind (PBIK) service. If you use this service and payroll benefits and expenses you won’t have to report them on a P11D.
If you do not register the benefits and expenses you intend to payroll you will have to report them on a P11D. However, P11D(b) forms must still be completed, including the total benefits and expenses provided, whether or not they’ve been put through your payroll.
If you payroll car and car fuel benefit you should not complete P46 (Car) forms as you will be deducting the tax due on these benefits at source.
Please see HMRCs website here for further details.