The windscreen is bonded in so it shouldn't leak even without the trim around the edge.
One possibility is the aircon drain and also this..
take off the passenger wiper arm and blade. prise off cover on arm to reveal 13mm nut, undo nut and remove wiper arm. (remember the cover might look solid, just push it off with your fingers, it's plastic, not solid and hides the nut)
remove the passenger half of the plastic sill that covers the bottom of windscreen to engine compartment.
3 require a star socket (99p shop) bonnet open.
1 screw has a plastic cover on it that you prise off with a screwdrive and then requires a phillipes screwdriver. bonnet closed.
what you will now see is a bulk head that traps the water, and is almost full of water if you have this problem. there is a drain point roughly in the middle, that empties into the engine compartment. put your hand in there (yes it's cold, wet and full of disgusting stuff) push your finger into the sludgey hole, and you will unblock it. water will spill out.
::: water was filling the bulk head and couldn't escape into the engine compartment as per design. the next escape point for the water is the passenger footwell."