Done this yesterday 150 miles from home and from the spare key -
Picture this, opened boot with remote, put luggage and jacket in boot, closed boot. Keys were in jacket.
Car was deadlocked. Called the RAC, RAC chappie says not much chance as Omega difficult to open when deadlocked, but any he forces top of door out a wee bit to try and press remote boot release. Nothing. Then uses various wires and around 20 mins later got the bottom open, tried a few things there to power up some things. Nothing. Pull the door release nothing etc etc.
So tried various things, I always deadlock the car and so it made things alot worse. Phoned a good auto electrian I know who spoke to the RAC chappie who was then quite chuffed when the doors all unlocked, so I can say you do NOT need to break any windows to get in even if you do not have the key and the car IS deadlock, it does not deactivate the alarm, you don't need to open the bonnet and it takes about 2-3 minutes, the alarm sounds until you get your keys, I won't be posting the HOW to though, sorry.