Well, thanks to Booths Motor Group at Tuggerah on NSW Central Coast, the engine warning light in my i30 is now off. Pat of me would have been happier if they'd actually found something wrong. They said everything is working as it should be and they think is was some sort of communications fault between the gearbox and the engine. They reset the fault and it's gone away.
Hmmmm........ Might have been more believable if they just told me it was The Flux Capacitor ;-)
Anyway, very good of them to fit me in without notice, though.
Will keep an eye on it and hopefully there's no repeat on the return leg of our trip.