I found this on the government site I hope it helps,
How to display
the badge
When using the parking concessions you
must display the badge on the dashboard
or facia panel, where it can be clearly read
through the front windscreen. If there is no
dashboard or facia panel in your vehicle,
you must still display the badge in a place
where it can be clearly read from outside the
vehicle. The front of the badge should face
upwards, showing the hologram. The side
showing the photograph should not be
visible through the windscreen.
You must also ensure that the details on
the front of the badge remain legible. If they
become unreadable through fading or wear
and tear, you must return the badge to your
local authority so they can issue you with a
new one. Displaying a badge that is illegible
may result in a parking fine.
Garnuft is right it should only be used if the disabled person is getting out of the car,