Hi everyone,
As a final last resort I thought I would get some top mounts from RPD. Fitted them and after a run around the block, the mounts are sitting as good as they did when I first got the car (i.e. correctly).
If it remains like this, then there are "OEM" rubber doughnuts in the market which are not to the same spec as those you get from the Renault dealer!
I hope this is useful for anyone else who experiences the same headache as I have had on this. Here's hoping it's finally resolved once and for all.
Thanks for all your help guys.