I've just got home and tried jumping it off a spare car battery I had lying around but didn't seem to do anything. I've just taken the battery out and stuck it on charge and the meter shows it was nearly dead but I'm worried that wasn't the issue as I'm sure I killed it trying to get it to start in the first place?
Keeping my fingers crossed when I try it again in a few hours
As for condensation.... there a good chance there was, the garage is free standing and has wooden doors so not air tight or temperature controlled by any measure