Earlier today I put my drivers window down and heard a few clunk's. Tried to put it back up and although the motor was working the window stayed fully down.

Got home and stripped the door card off and removed the regulator. It seems that the window isn't stopping when it gets to its lowest position and causing the regulator to go too low and not have any teeth left to raise the window back up.

My question is, what should stop the window at its lowest position? Should there be a bump stop of some kind?

I have managed to refit the regulator and it is all working fine, unless the window goes fully down

I dont think there is a bump stop.
When resistance is felt either fully down or fully up a signal is sent to the the BCU or ECU I believe cant remember which one.
Looks like your regulator needs to be changed, not very pricey, I shyed away from the cheap new ones and went for a good used 2nd hand as thaty way your more or less guaranteed on getting a genuine land rover one for not much money but run the risk of it not lasting. Mine has lasted well.

Its the BCU

Thanks for the quick reply, will have a look and try get a decent 2nd hand one. In the meantime I think I will put something in the bottom of the door to stop the window going too far.

Cheers