|image from Screwfix|
Then it stopped. I oiled the blades and spent the next 20 minutes trying to restart it; eventually it fired up and I was able to do another 20 minutes of hedge trimming. And then it stopped again. This time I gave up after five minutes as it was getting dark.
Tomorrow I'll check the spark plug. If it seems OK but the trimmer still won't run properly I might have to phone the helpline before returning it to Screwfix.