"And here's one I've already made."

A la Blue Peter, but featuring no sticky backed plastic!  I made and painted this kit around ten years ago before my kit making lurched to a halt. The box is long gone and I've spent a lot of time today trying to discover this aircraft's provenance, without success. Airfix don't appear to do it now. Does anyone know what mark of Spitfire this is, and what the markings mean?