I understand your confusion with identifying the door leaf you came across during your Fire Door Survey.
I have come across similar types of door leaves in the form of uPVC French doors, which are quite popular these days due to their durability and easy maintenance. The solid timber core provides added strength and insulation, while the uPVC fascia gives a modern and sleek appearance.
Regarding the manufacturer, it might be worth checking with local suppliers and distributors of uPVC doors and windows in your area to see if they can identify the door leaf.
Hope this helps, and good luck with your survey!
