Thanks to help from MadNoel10, I've had some success with this.
The reluctor ring for ABS has snapped. This a toothed ring that attaches to the hub and sends signals to the ABS sensor.
Renault told me that I would have to get a whole drive shaft, but have been able to source a new reluctor ring on the web from...
Nigel Thompson Transmissions in Leeds tel 0113 289 0819
This bloke was really helpful and was able to supply one delivered for £32. Apparently the phase 1 scenic have a 44 teeth ring. Hopefully it is the right one. I was quoted 1 hours labour to fit it as the drive shaft has to come out and the new ring is 'drifted' on.
It appears that this is a very common problem on Meganes and Clios of this era.
Rings and info are also available from http://www.reluctorrings.com
I'll repost when it's finally sorted.
Now onto next issue. Bad earth in rear lights