They are rare guns, most shooters won't know what they are - the fixed-barrel version of the BSA Spitfire. I think I sold my excellent condition .22 for £250 years ago. The two calibre one is probably worth more.
Probably about £250 with the pump, if you have the 14mm scope mounts for the MaxiGrip rail then that would add something.
An interesting design which should tempt the PCP collectors (do they really exist) as it is a unique design.