Sorry - really boring, but I wondered if anyone could help!

My 12 year old Peugeot 206 has got a very intermittent overheat problem. Whenever I take it to the garage, they can't get the fault to reproduce. I drive the thing every day and it probably happens once or twice a week, always in traffic.

I have recorded what I see and have uploaded it:

http://www.youtube.com/watch?v=lCbno...&feature=g-upl

My first suggestion would be a fan problem or thermostat...but I am unsure because of the way it overheats (watch the youtube video at about 0:38 - it hangs at 95 degrees then shoots off the scale only to recover fairly instantly when I put the heating fan on.)

Can anyone diagnose this from the video?

My apologies for the 'soundtrack'!