I'm not sure if anyone on here will find this useful but there doesn't seem to be a huge ammount of information floating around regarding this so I thought I'd contribute.
Right, so this is basically a guide on how to replace the original firmware on your LG Optimus 7 (assuming it's branded by Orange or Vodafone). Unlocking it with a code works fine if you don't mind the apps and branding that the network providers have put on there staying. Note also that you will still need to purchase a code to use a giffgaff SIM.
Prepare your phone:
Go into the MFG app (developer menu) by dialling in ##634#
You'll be asked for a password. This is "appmfg#*#" in numbers, so "277634#*#"
Go to "Engineer Menu > Port Setting > USB Switching > QC Composite" then let the phone reboot.
and the phone is now ready.
Download LGDP2 V36 UMTS Setup and extract.
Install the .exe file in the "LGDP2_31_INCLUDE_LGDP1_Setup" folder and when it asks for a serial use the one provided (the text file)
Go to the DOWNLOAD folder and copy the files to C:\DOWNLOAD. If it's needed then overwrite any files.
Download LG United Modem Driver and install. Connect your phone to the PC. The appropriate drivers should install. At this point you should also go to the Device Manager and check which COM Port has been assigned to the phone, it will be needed later.
Go to C:\DOWNLOAD and open "LGDP2_V36_UMTS"
it looks intimidating but there isn't much to it.
In the "Division" menu selct UMTS, then OK. Ignore any error messages that come up at this point.
Using Easy Select choose the appropriate range of ports (that includes the one assigned to your phone) or just manually select the correct ones.
Now select your DLL (make sure it's the right one)
and firmware (.DZ file) by clicking RUN DOWNLOAD CONFIGURATION
Again ignore the error message, and click START in the upper left.
Now turn the phone off. Turn it back on and plug it into the USB before the Windows logo appears. It should enter emergency download mode by itself and start to flash. It might take a few attempts before it enters emergeny download mode.
After around 5-10 minutes the phone will restart. Once restarted you can press STOP and unplug the phone. Now you should have a working phone with no branding (: