This is an extremely nice, original RAF Spitfire mirror, part number 27H/2017.
As a sign of the naivety of Fighter Command at the onset of war, early Spitfires were not fitted with mirrors. Quickly the pilots learnt to 'borrow' mirrors from their cars and have the riggers fashion housings to keep them in place. Soon the Air Ministry had official mirrors manufactured and this is an example of one of those.
Fixed by a stalk to the front screen frame, this carries the correct Air Ministry stamping and part number. This really is a lovely example without the usual micro cracks so often seen around the screws.