Your description is not quite clear enough for anyone to help. You say "locked out" but in the title you have "Immobilizer". If your battery is dead and you cannot unlock the car that does not mean the immobilizer is activated. You need to get the battery charged up. I understand it is possible to unlatch the hood from beneath the car by poking around the two latches. I have also read of someone connecting a charger to wiring at the tail lights. Try searching
www.rangerovers.net
as this is where I am getting my info from.
If you get the battery charged you should be able to use the key to open the car and try to start it. If you get the "engine immobilized" message on the dash display that is another bag of worms and the dealer is not likely to be able to help you. There is another code, the Emergency Key Access code, EKA, that can get an immobilized engine going again. How to use is described in the manual. Code might be 1515. If that does not work you may need to send the BeCM to the UK to get unlocked.