Here's a good one! Muppet me!
I bombed home to re-fill yesterday lunchtime, connected up hose from storage tank (200L) to empty tank in car (125L). Takes about 10 mins. My cuppa and lunch take 20 mins and with an "Aaaaaaaaaaarrgh!" of Beano or Dandy proportions I run out to car realising I have forgotten to turn off the hose. :

Car is on a sloping drive facing downwards and water gravity leads excess 75 litres to form a footbath in the front passenger footwell before leaking out through grommet holes.
Curses! So I syphon out the worst of it and decide to go off to work about half an hour late. B-b-b-b-b-b-bip! Starter spins but no engine firing up!

So, check for spark - all ok on all plugs. Undo fuel filter union feed bolt and fuel feed OK. Fiddle about for an hour and call garage. "Bring it in tomorrow (today) mate!"
Late last night, car starts but pops and splutters and dies and the engine management light stays on. This morning, seems ok but missing, put bike in back and I nurse it to the garage, post keys and cycle home.
Just had a call from the garage. "Nothing wrong with your car..by the way the front carpets are soaking."
"Yeah" says I and explains about tank overfill and sorry for the stinky smell etc.
"Hang on" says mechanic give me five minutes and I'll call back
Turns out that Honda put an engine management sensor under the front carpets and this had soaked through and was giving false readings to the engine.
Garage are drying out car with a fan heater this afternoon!
As Sherlock Holmes said "When you have eliminated the improbable then the impossible must be true!" (Loose paraphrase)
Duuuuh!