That has to be UPVC as you can see the moulding and the polystyrene inside the door, if it is an infill panel you could possibly replace it but you would need a repair specialist to check it out.
Are you in Liverpool as the is a specialist repair firm on West Derby lane just before Belmont road by Panorama kitchens called Home Secure.
http://maps.google.co.uk/maps?hl=en&...95039145258196