I have exactly the same problem as you and im waiting on a fix.
I have a 1999 Clio 1.2.
It could be the starter motor or the solonoid attached to it thats at falut. I was also just informed on my thread that it still could be a duff battery even although it appears to be ok. So im gonna get that checked tomorrow at local garage.
It wont be the
sensor so ignore that. Ive had mines out around 3 times and cleaned it, to no avail. Anyway, the
would only be at fault if your engine was trying to turn over. So you can count it out.
I also replaced the connector to the solonoid (a common problem with Clios) but it didnt fix the problem. Replaced key fob batteries too (dont know why) but no use.
Do you have to try for ages before it starts? I had to turn the key around 50 times the other morning before it started! BUT, last 2 mornings has been startin 1st time as the weather has been mild! Strange....
The car is fine when its running, its only when it starting from COLD that i have issues with non starting.
Let me know how you get on as i have identical problems as you!!