Local bodywork repair centre inspected the car and said that the problem was one of paintwork and not corrossion from underneath.
I do have confidence in their judgement and accept their informed view that the problem is one of paintwork, probably due to the action of pollutants (say birdlime or the like) which through time has become visable.
Never-the-less I rang
Renault customer services
expressing my concern that a "blow-in" repair had been carried out pre delivery of the car from new, without my knowledge.
Renault Customer Services
manager undertook to investigate. A few days ago he called to say that the Renault accident and repair inspector judged that it was paintwork issue and confirmed the evidence of a blow in repair. However, it was not possible to establish the history relating to this, especially since the Renault dealership from whom I bought the car was no longer in business.
Like my local Accident and repair centre Renault did not foresee any future problem with corrossion, but to get back to them if at sometime in the future I had any cause for concern.
So I have to accept that I am not covered by any Renault warranty.
The knowledge I have gained through this website has been a bit of a eye- opener, especially in regard to the perfection, or should I say inperfection, of new cars and the unsuspected bodywork rework that can and does occur on your spanking new pride and joy.