Thanks guys,
Here is where the smoke came from:
Smoke drifted really slowly like someone slowly blowing out some cigarette smoke loop in slow motion (nothing fast/"jetting" or shooting)
Small ammount and didn't last long as the second I noticed it I shut the aircraft down fully (as the ignitions right in front of me, it didn't have time to build).
If it was a fault at the switch, why would it not also produce smoke on my 2nd start-up?
Is the potential oil leak of any significance? or a red herring?
Someone is flying the aircraft tomorrow and 3 people on Saturday, I'd be interested to see how those guys get on.
Also after it occured, an expereinced instructor looked underneath and couldn't see anything at all/there was nothing off when I looked at the engine briefly when checking the oil)
Everything I'm saying is 100% the Truth but I could tell he didnt' believe a word I was saying today, (may be because once before I had a 0 reading Ammeter (also on an away flight) and had to speak to our Radio room people prior to flying home, this was in case I lost Radio power and needed to join the circuit without communicating so they could anticipate it), but he asked me if I "fly to places and then get nervous about flying home..." I told him that the zero reading Ammeter (which may have simply been the instrument at error I appreciate) was visible to everyone else eg: engineers, insructors also and not connected to some "nervousness"