Pat thanks for your interest in the diagnostic kit we have on loan but I am afraid I am not a Renault Technician so travelling to MK from Ipswich seems it may be a waste of your time.
However reading through your plight I see that the problem has been fixed once before with a replacement part.
We do have details on where to find the various parts in the engine bay
Once again this can be found in the knowledge base section of the forums
Laguna -> Engines
It would be wise to find out exactly what sensor was replaced and check that the plug in electrical connector is not loose or has corroded or weathered contacts ( if so rub gentle with emery board to clean the metal contacts )
Sorry if that sounds like I am teaching you to suck eggs..
Please reply if you need any further info ( I have subscribed to this thread with an email alert so I can catch your reply )..
Maybe you feel just clearing the error code will fix it ? If so take it back to the guy who did the work and get him to clear the code..