Check your scuttle panel, right in the corners, there'll be a small drain hole. There's a drainage pipe that runs under the wheel arch from that hole and if that's blocked, which they tend to do after a while, the water won't drain from the scuttle and it'll enter the car.
I had this problem on my MK2, so cleared the drain with some stiff electrical cable by pushing it down and rinsing with a hose.