Brussels allotments: bartering

I read an article in a Belgian magazine some time back about allotments (in Uccle, I think) where in return for helping out you earn some of the fruit & veg. I'm really interested in taking part in such a project, as I want to learn how to grow my own and would love to have organic fruit and veg, for free in this case. Does anyone in Uccle or surrounds happen to know where these allotments are? Or if there are other allotments working on the same bartering principle? Many thanks in advance.