I posted about this a while ago, as not riding for months my tack has just been sitting aroung. I was told not to use glycerin saddle soap, so have changed to a leather tack cleaner (sorry cant remember which one) and that seems to be doing the trick.
Mik, you're from Spain aren't you? I guess you don't have as much cold and damp as we do over here. We are pretty used to it! All tack gets the green mould when left in a cold, damp tack room untouched for a few weeks.
Just clean it as normal, it'll come up good as new.