Chère Tricy,
One more thought. It would help if you could remember the year or maybe even the channel on which you've seen this film. Was it 30 or 40 years ago, before all the private channels started their programs? Then you would have to deal with only a handful of channels and in that case there should be a way to find out your movie title.
Other than you there is one more French person in tvforen.de, his user name is SAS Prinz Malko, he might be able to help you with determining on which channel you might have watched this film and to figure out if it really was British childrens film from CFF (Childrens Film Foundation). I know the CFF movies were extremely popular on German TV in the sixties, but I don't even know if they have been aired on French TV.
Even if SAS Prinz Malko does not know your movie, he still might have more knowledge than the two of us to check some French website with old TV programs. Such a website is in existence in Germany, but I wouldn't even know the correct keywords to google it in French.
Je suis désolée,
Chrissie
PS: Did you write to my friend in England? I contacted him last night, so he is expecting your movie description. And did you read the plots/summaries of all CFF movies in the CFTF website link that I gave you a few weeks ago?