If your car has a sunroof its drainholes could be blocked. Sunroof on our 145 has drainholes in the front that drain down the windscreen pillars into the scuttle and in the back that drain out if the back of the roof. The two front holes blocked, the sunroof tray filled and drained into the headlining then into the footwell. Try pouring water from a jug into the sunroof tray to check this out.
If the 146 is the "same" as the 155, there is a drain hole under the windscreen wiper plastic on the left hand side and it becomes blocked with leaves etc. This has happened on a few 155's, so just an idea as I don't know the ins and outs of the 146.
There is always the possibility of rust eek!
sorry I said it, but if a panel is rusted through (not necessarily holed) it could capilliary through - a long shot I know, but it happened on a Mini I had once - now RIP 'cos the rust just wouldn't stop spreadin'!
If you have 'pourous-backed' carpets, this will exagerate the capilliary effect.