Had same happen to me last year with a Citroen C5 saloon, we had driven around 80 miles and had just pitched the caravan when i threw the keys on the drivers seat and closed the door to remove the towing mirror, the car locked itself and after bouncing the caravan wrench off the passenger side front quarter window. only just about marked it. Had to call out the breakdown services.
A right miserable bloke came out and forced small nylon wedges into the top rear corner of the drivers door,then slipped one of those little baloon things in, inflated it a bit to ease the gap open a bit more,then used a metal rod to pull on drivers door pull.
Looked very damaging what he was doing but the car recovered from it.
Don't know if you could do this on a discovery.
Gary