Hi Ian and Kevin, thanks for getting back to me, I came in this morning to check both of your suggestions. It appears that I have intermittent comms fault with the bsi. It will connect and then drop out. How this causes the n/s sensor to read over 1000mph i'm not to sure but will dig further.

Kevin it was an exact part number match, but will call citroen today and see what they say.

Thanks again for your help and hopefully will have a fix for this soon.