Oh! I didn't see your picture! Yes you probably could use the same charging circuit, but since you now have information on the origin of the battery you should try contacting All batteries UK to find out if they still carry this item.
Hopefully you can re-purpose the casing to hold 8 new cells (Alkiline or NiMH). If you want new NiMH cells, you will have to remove the individual cells from the casing again to re-charge them on a third-party charger.
I'm surprised the camera doesn't have standard alkaline battery contacts...
Two of the three pins are your positive and negative terminals and the third is most likely a thermistor terminal for monitoring temperature. Have you measured across all combinations of the three terminals? The highest value you measure would mean your measuring across the + and - terminals...
Is this your camera?
http://www.e-tell.info/myact/doc_man_lincs/argus thermal camera.pdf
If so, 12V makes sense since it runs off of 8 AA batteries (8 x 1.5V = 12V). The rechargable pack was an accessory but the datasheet isn't specific. Judging by the age of the camera, optional rechargable...