I delocked the front doors of my old blue Carlton years ago. I did not delock the boot though but instead put a reasonably thick black sticker over the rectangle push button thing so it "looked" delocked but I could always peel it off in emergency. Never had flat battery to deal with but did have a blown fuse which made me thankful I did not delock the boot.
I did think though that if I did delock the boot I would build in a secret flip switch somewhere under the bonnet to activate the C/L in case of failure.
If the worst comes to the worst, smash the small rear triangle window (like this
http://www.ebay.co.uk/itm/WINDOW-GLASS-LH-C-pillar-1-4-light-Carlton-Mk-3-/360247181899?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item53e067c24b) then use a snooker cue to flip up an inner lock. There should be plenty of spare triangle ones on ebay or via this forum (check first

!) and they are reasonably easy to remove and replace.
I have one or two knocking about in my garage.
From what I can remember its just a couple of posi screws and a 13 mil bolt to remove / refit?