I seem to have sorted (touch wood) my drivers footwell leak, however have stuffed plenty of news paper into the passenger (drivers side) footwell and that seems to be soaking up quite alot of water.
i would definitely recommend taking out the plastic on the wheel arch and cleaning out all the gunk there, so the water runs straight through. The water comes from just below the windscreen and runs through a small hole inside the plastic casing(that can easily be blocked with leaves and gunk). I forced the plastic casing open and put a block of wood there to keep it open whilst i stuck my hand in and tried to remove leaves etc.
The water runs down and out of the wheel arch. I removed a solid 3 handfuls of gunk from inside the plastic arch ( a heck of alot) , and then ran some water through to clear the remaining gunk. Cannot confirm yet if this is the cause of my leak, but will update you if it dries out.
Other things i have tried so far;
sun roof drains
door nipples
I also have most of the carpet up, and if we get some good weather soon i am going to take out the drivers seat, and get fully under the carpet, and have my other half throw buckets of water until i can see the water seeping in.
Apologies for some of the terminology im not sure of the correct term for the plastic casing just below the windscreen!