As a result of this thread I decided to check my oil for the first time since I bought the car 3 years ago. I was surprised to find the dipstick handle at the top of the engine, but of course it turns out to be a very long stick! I did it according to the book, hot engine, level ground, 3 minutes, wipe the stick etc, but I found it quite difficult to see the level. The oil was changed only 3 months ago, so is quite clean. Anyway, I don't think it was above the top mark, and I don't suppose I'll ever check it again unless a warning light appears.