Hi, I wonder if you can help me out

Basically, I posted a while ago about an Omega Elite and am now looking at selling or breaking the car

. Unfortunately, as it has been stood for so long, the battery is dead (if connected) and the door will not open on the key. The boot lock failed a while ago and was never replaced as it wasnt used.
I have tried the key several times whilst pulling the handle but no luck, the key turns to the left as far as it is meant to but I darent force as its only 1 key. I have also just seen a post advising to place jump leads to the starter motor to provide power to open the doors? If the battery is connected then hopefully this will work but can somebody advise on where the find the starter motor from underneath and where should the positive be connected?
I also know that it can be done through the grille. Now this is obviously a way that probably should not be on public forums. Ive got so far with his but cannot get to or find the cable. If somebody could maybe point me in the right direction via quick reply to be removed or by PM it would be much appreciated.
We are hoping the battery is still connected but due to it being off road, I have a feeling we disconnected it after locking the car up without thinking it would be left so long.
Any help or info appreciated!!
Thanks