Renault Safrane, 2.0 lt RT L reg, , this car did drive sound,

What were the circumstances of this incident? Did you just wake up attempt to drive off and it wouldn't work? Or did it cut out on you?

Was the battery actually flat or do you have no way of checking?

Have you tired using a different battery or is the current one definitely holding its charge?

See if you can locate schematics for your installed immobiliser, and try and disable it.

Does the engine turn over? If not check the wiring for damage or loose connections, the starter motor could also possibly be shafted.