Ian,
From my experience in the lake country of New York state our family post & beam frame (circa 1804-11) started to suffer from sill plate moisture invasion in winters to -20F. Over the years my brother and I had to selectively replace sections of the sill and the external waterboard below the clapboard siding. When doing this renewal we put moisture barrier from two courses of siding above the sill down over the sill and held in place by the new waterboards. We still had minor condensation on the stone foundation but not the rivers we used to have. My recent experience here in VA with northside (no sun) mold on both exposed wood and aluminum siding has created several lessons too.
Because of your northern latitude you can only do interior first aid until late spring.
Spraying with Clorox will help retard mold growth.
In the interior air space get a dehumidifier and an ozone generator air purifier running ASAP.
Scrub and wipe after your initial spraying then spray again. Wear rubber/plastic gloves to protect your skin along with some goggles for the eyes.
Not knowing the structual details of the wall/floor fit chat with some local builders about their techniques to avoid moisture penetration. The retrofit will not be easy or cheap.
I hope this missive is not discouraging.
deralte (aka Emmett)