Sorry, I didn't say anything else about this. Had a mobile mechanic mate come out to me and have a look. Ran all sorts of diagnostic tests using his fancy Snap-On Diagnostics Unit and got absolutely nothing!
He then was able to start it up using the Diagnostic Unit and its been fine since?!?!?!?!?!!?!?!? He's never seen anything like it and can't think what the problem was/is, but now its completely fine!
Hoping that it doesn't happen again.