Most of the times, when I put on my indicator to turn left, it does not diesengage after completing the turn. This basically happens with all the gentle corners or at traffic circles. If the turn is fairly sharp there's no problem - it clicks back. The right side works ok under all conditions.

I imagine that it should be something that has worn down, but I have no idea what to look for. I'd like to resolve this, as it is rapidly becoming a major source of irritation - especially when you discover that you travelled a couple of Km with the blasted indicator flashing away pointlessly

Any suggestion on how to resolve this?

It sounds like the cancelling mechanism is at fault. This is made up of some small plastic parts directly behind the steering wheel. Should be reasonably easy to access, you will have to take the shroud off. Obviously proceed with caution or get a garage to do it if your car has an airbag.

The steering wheel has to be turned beyond 90 deg from the straight ahead in order for it to cancel when turned back.

Test yours in both directions while stationary to see if it truely is faulty before wasting money on a new column switch.

If I turn left, the wheel definitely needs to turn more than 90 degrees for it to disengage (more like 120-130). If I turn right, even about 60-70 degrees will disengage.
I changed the airbag about a year ago. Is it possible that when refitting the steering wheel the mechanism went 'out of alignment'?

Cant help you, but your not alone. My Punto is the same, if im turning right i have to hold the damn stick to keep the indicators on when im going around a roundabout, yet when im going left i have to turn the indicators off myself!

Bloody annoying!

Mine self cancels but the beeper is so quiet and warning lamp so dim I dont always see its still on. Its embarasing (SP?) and easy to do on the M-way.

This looks like the best option.