Substantial, 200-300 Nm usually. Check with a dealer or get the Haynes manual for the car. I use a scaffold tube and a 1/2" drive socket for these nuts, then make sure they are fully home with a short drive bar and a hammer. Err on the side of over torquing.

Thinking about it more, what I do is stand on the scaffold tube with it horizontal. I know my weight and I stand at the distance along the bar to give the right lever arm corresponding to the torque figure.

 

thanks for the reply.

in the end I went for "as tight as I could go with a 2ft bar" nm.

Hopefully that will suffice

 

Try standing on the bar and see if the nut can still move. It shouldn't. This link might be helpful? http://www.renaultforums.co.uk/showthread.php?t=83784