I had this a few weeks ago and found it to be due to a dodgy soldered joint within the flasher module. I managed to repair mine, but a complete new flasher module costs £31 from stealers.
The flasher module is located behind the hazard warning button in the centre of the dash. Unfortunately, you cannot simply slide the module out and put a new one in. I found that the stereo cage is in the way, so you cannot unplug the module.
If you're feeling brave, you can remove the glovebox and the trim under the steering wheel, which allows access to the screws for loosening the centre part of the dash. You can then remove the centre part of the dash (after you've removed the stereo and a load of screws), allowing access to the wiring behind the flasher. You can then unplug wiring, remove module and fit new module.
Took me a couple of hours and has been OK since. /ubbthreads/images/graemlins/groovy.gif