The drum brake is adjusted through a small toothed wheel you access from the inside of the backing plate, and often will be seized up or just plain useless, so taking the whole thing apart cleaning it, freeing it and sorting will help you achieve better hand brake operation (And help you pass MOT) however there is something that seems to rust and fail. The backing plate.
On here you can see the two brake pads at either side. These have a pivot point in the middle which is held in by a spring and a pin with a forked end and spade fitting. The idea is you push it on (allen key) against the spring push through a slot and twist to lock it.
That's the spring and the pin you can see the wide end to the top of the photo that pushes into the backing plate to secure it.
And now on mine below you'll see the problem:
That hole rusts and becomes wider, eventually the pin just pushes straight through and stops holding the brake pad in place, rendering it useless.
Panic then sets in as you need to replace the whole backing plate, which would be a pain as taking the hub off and all sorts! Replacements are also difficult to find and expensive as it's a whole chunk of metal and depending on what you can find may require the bearing or not. Either way it would be tricky to replace and could be pricey.
Below is one I'd found on ebay:
So what is the solution? Some cars have a similar design but have a slotted washer that goes on the rear of this backing plate to act as the binding point, this seemed ideal as a retro-fit, so a slight modification of it (Flattening it out) and that works great. At the same time using different springs helped as the standard fitting kit for rear brakes has a spring that at fully compressed is only just the right length to let the pin push through, a different compression spring works better allowing the pin to push through further and get a better purchase without as much tension on the spring.
This is what we used, unfortunately I don't have a reference for them as they were in my dads pile of bits from other cars and jobs in the past. We flattened them in the vice and they worked great for this!