I've had the EML on a few times since I bought the car, staying on for no more than a minute, sometimes just for 10 seconds. Sometimes it would go out if I stopped and then re-started the car, sometimes it wouldn't and would just go out of its own accord later. I didn't think anything of it and put it down to the car getting hot or something.
Late last night, while driving along the motorway, it came on and stayed on for about 2 minutes and has been randomly coming on for a minute or two since. When it is on, it has obviously gone into the 'limp mode' as there is very little power available. There seems to be a
slight correspondence between slowing in traffic and the light coming on, but it is by no means repeatable - it's just an impression. Last night it was coming on for 30 seconds or so even when doing a steady '70 mph'

I thought I could do the paperclip test but having searched on here, my car is too new for that. Vauxhall want £40 to diagnose it just by plugging the car in, so I'm looking for suggestions of what to check first before I go down that route.
There is very little written on here about the DTi engine, so I'm at a loss at the moment.
99% of the time the light is off and the engine is running fine. There's no smoke, no rough idling, no loss of electrical power, the engine doesn't die - the light just comes on and the engine seems like a non-turbo.
Help!
Also, does anyone know of a good alternative to Vauxhall in the Yeovil area to diagnose the problem if it's not something silly like a loose connection somewhere?
Cheers,
Graham