Just reporting back now that I've finally managed to have my C3 looked at, in case its useful info for anybody in the future. The engine management light decided to stay on permanently and the cutting out got worse so I took it in to the garage this morning to have the diagnostics read. The scanner came back with P0201 - injector control 1 oc or 5c and P0300 - misfire on one or several cylinders. Turns out the fault was caused by a missing retaining clip. Total bill was less than £60 and most of that was for the diagnostics. I took it for a test run around town as there's one thing we're not short of here and that's roundabouts, traffic lights and heavy traffic. All driving lovely again, thank goodness!