I'm a bit miffed at the moment. I just retrieved my Blackhawk / Night-Ops torch from the central console to find the batteries are totally dead, after no use at all

I'm not sure how that's happened, but I'm assuming the tail-switch has been pressed and drained them. I've put new batteries in and all seems good, and that leads me to my question....
Here in the UK, what's the cheapest method / source for CR123 batteries? I know nothing about these things at all, so any advice / pointers gratefully received - thanks
