I tried opening the pic in Paint Shop Pro to try to read the serial. After a couple of beers, I'm almost able to be certain that I imagine I can read "834x". There were Mk. II's with sn P8340-P8349. After some more beers, I found that JZ was used by 57 OTU.
In Morgan/Shacklady's Spitfire The Story I look for the common denominator: P8340-8349, and 57 OTU, and find these planes:
P8342 Ceram (to 57 OTU 31-3-43), P8343 Medan (to 57 OTU 10-4-42), P8344 Orkney (to 57 OTU 8-10-42).
On the other hand, the serial could be something completely different...
Edit: seeing that the original poster is Polish, I noted that one of those planes spent time with a Polish unit; P8342 wore UZ-N while at 306.