Hello Paul,
i will begin to study in Wrexham in September and i'm excited to see UK electrical things
The power plant bus bar colors and the green wire in that box belong somewhat together.
It seems to me there were 2 different color codes used at the same time. One was black - black - blue and the other one was yellow-greenn-purple for L1,L2,L3. I have seen yel-gn-pur in substations mostly, not in houses. I will try to find out more. In the house where the wirenut picture is from, they used yellow for switch to lamp and green for light relays interconnection.
Double insulated bonding cable: It is permitted to use single insulated gn/yel wire, also fine stranded ones, if it's in a pipe or raceway in or on a wall with only short portions uncovered (i.e. round a corner) and no danger of damage. Runs on a wall with clips like the picture shows (and a bit too much distance between clips...) demands for double insulated.
Switch/Socket combo: yes, you have to align the modules to each other. Thats easy by aligning the sheet metal frames together. The Cover Frame is held in place by a clip that goes into these 2 round holes at the switch, and by the socket cover itself at the socket. The GND bars help to get the socket cover on and find the thread for the fixation screw in the middle. That's pretty easy after youve done it 5 times.
