thickening fruit flan filling

How about Dr Oetkers vege gel sachets? Substitute the fruit juice for the cold water. It does set rather stiff, so perhaps you could use it more dilute than the instructions.

Does anyone remember that special stuff for flans, think it was called Quickjel?

Over here it would be on the baking shelf in a little tub like bicarbonate of soda and baking powder.
Hope you find some - otherwise cornflour is OK, or reduce some juice right down?

I'm going to try to find some tomorrow, but don't think I've ever seen it here. It's not even in my french dictionary. Liguee - marante, or fecule d'arrowroot.

Always use arrowroot, very successful

Yes, arrowroot works well.

A small amount of cornflour does work but it will make the sauce a little cloudy. Arrowroot is better as it stays clear.

Arrowroot is better than cornflour Tricia, it gives a clearer gel.
Cornflour would work though if you can't get arrowroot.