Make sure you have a signal from the key,as the circuit board can become damaged sometimes.If it does give a signal,then you'll need a reciever.They're around £60 new from Renault,and if you quote the number on the small sticker that is on the reciever they can match a new one to it,so it doesn't need reprogramming.Make sure the old reciever hasn't been damaged by water ingress through the aerial or sunroof.
Many thanks to you both.. I will order a new receiver, but how would I test if a signal is being sent out? The red light flashes when I press the button
There are immobiliser overrides available on ebay..
I've never heard of the immobiliser overrides before,so I can't comment on them.They do seem a little pricey,though.
Most garages will have a signal tester,and it only takes a few seconds to carry out.Apparently you can also test them using a digital camera,but I've never tried this.Apparently as you press the key near it the signal will effect the screen image so you can see if it's emitting a signal or not.I've also been told that some key signals can be picked up using a radio aerial.(it causes interference to the radio when worked).
To order a new reciever from Renault,you'll need to remove the old one and quote the number on the sticker which is stuck on the unit.Dealers can usually get them the next day.