intermitant starting!!!!!!!!!!!!!!!!

[gav78]

I have a 172 cup which at the moment is intermitenly starting. When it decides not to start the imoboliser light flashes really quickly and then wont turn over to start!!! It happens when its cold or hot, driven a short distance or long distance, driven normally or like you stole it!!!!! its had a new bsi unit on ecu code reader and a new key and it still does it!!!! I just had it at renault for a week and they couldnt find a fault as it didn't do it all the time it was there!!! My patience is wearing very thin