The P46(car) form is used by employers to send in details of company car changes to HMRC. This used to be a manual process that was undertaken at the end of quarterly periods (5th July, 5th October, 5th January and 5th April), however with the greater use of electronic submission via the Government Gateway (File by Internet) the process can now be undertaken as frequently as needed.
The sooner a P46(car) is submitted to HMRC, the sooner and coding notice change can be applied for an employee.
An ‘electronic’ P46(car) can inform HMRC about a car being provided, replaced, or withdrawn, however a paper P46(car) can only inform of a car being provided or withdrawn, so is less flexible.
Please note there is no equivalent of aP46(car) for vans (Section G)