I don't know if you have solved the problem but I had a problem with my previous Clio (2001 model) that sounds very similar. Even from new there were occasions when nothing happened when the key was turned - although after between 10 and 20 attempts it usually started fine. It was very occasional which made taking it back to the dealer pointless

. Just before the warranty expired at three years I did ask them to look into it as it was getting more frequent and they diagnosed a faulty immobiliser transponder (possibly the wrong word, my memory is vague) - i.e. the part in the steering column that recognises the key and switches off the immobiliser. They dismantled the steering column and replaced various parts.
The problem still persisted and got more frequent :steam: so I also called out the RAC in desperation one morning when the car wouldn't start. The mechanic also suspected the immobiliser and spend about 3 hours trying to bypass it. In the end, he gave up and suggested taking it back to the dealer. He was about to leave when he had a final thought that we were all blaming the wrong part. He went back to basics and got me to turn the key while he thumped the starter motor...and the engine burst into life. In the end it turned out to be a sticking starter motor! I drove around for a while with a hammer and chisel until Renault managed to replace the starter motor. After that...no problems at all :d .
A long story, but retold as the source of the problem was totally missed (and would have been expensive in my case if the car was out of warranty).
My suggestion...if it is still happening, try hitting the starter motor while someone turns the ignition. It may be the same problem. Then again, it may not....