The Highest kill of WW2 was done in a Spitfire MK VII which was a MKV fitted with a Merlin 60 series engine and extended wing tips and fully pressurised. The Spitfire shot down a high flying Junkers JU86 at 46,000 foot. The Germans gave up high flying Recce sorties after that as it came as a bit of a shock to be had at that hight.
Spitfire MK VII was a imporved Spitfire MK VI which was not very good and needed the pilot to be bolted and sealed into his cockpit. The system used on the Spitfire MK VII was used again on the Spitfire
PR MK XIX which could at a push operate at 50,000. PRXIX were
PR version of the Spitfire MK XIV which again was a Spitfire ML VIII fitted with a Griffon engine.
Previous record was 41,000 in a modified Spitfire MKIX before the MK VII entered service flown by F/O Prince Emanuel Galitzine of Special Service (High Altitude) Flight Northolt, September 1942
Before anybody asked why did the MK VII enter service after the MK IX, basic interceptor Spitfires in Fighter Command during the war were as follows in order they entered service.
MK I/II
MK V
MK IX Stop gap Fighter (MK V fitted with a 60 series engine) until the MK VIII (new airframe) entered service but the RAF in the UK were so happy with the MK IX that they did not need the MK VIII.
MK VII (MK V fitted with 60 series and extended wing tips)
MK VIII These were given to the USAAF and RAF sqns in the Middle and Far East.
MK XIV (MK VIII fitted with a Griffon 5 bladed) to shoot down VI or Diver Patrols)
(Note) Spitfire MK XII was again a MK V fitted with a early short Griffon with 4 blades but was very rough and only served in 2 Sqns one being 91 Sqn for only about 4 months or so before being replaced with MK XIV March 1944.
(Note) Spitfire MK XVI (the new one being restored for the BBMF) this was a Spitfire MK IX fitted with a US Built Merlin from the P51D due to the fact at that time we could not build enough Merlins with production demands for Lancaster and Mosquito. These were mainly used in ground attack roles, but in their low back version used to replace Spitfire MK IX in the air combat role towards the end of the war.
Lanacaster lovers note Lancaster B Mk I is a Lanc fitted with British Built Merlins, B Mk II Fitter with Bristol Radials and the B Mk III Lanc fitted again with US Built Merlins.