Ham and pickle is the ham sandwich answered with Branston, and in British usage the pickle is almost always that one specific thing: a dark, chunky, sweet-and-sour brown pickle of diced vegetables in a thick, malty, tamarind-edged sauce. That is the variable the whole sandwich turns on. Cooked ham is salty, faintly fatty, and texturally flat, and Branston meets all three of those at once with a sweetness the meat lacks, an acid that cuts the fat, and soft diced vegetable chunks that break the monotony without ever being crisp. The defining contrast here is sweet-sour against salt, which is a gentler, rounder answer than the hard mustard heat of piccalilli, and it is why this is the version that reads as comforting rather than bracing.
The craft is the measured smear and the barrier underneath it. Branston is wet and sugary, so it is spread in a controlled layer rather than heaped, because too much of it slicks the ham, soaks the crumb, and pushes the sandwich into jammy. Butter on the bread is doing structural work as the seal that keeps the pickle's vinegar and sugar out of the soft crumb until the sandwich is eaten, which matters more here than in a dry build. The ham goes on thick enough to carry the sweetness rather than be swamped by it, and the bread stays soft and plain because the pickle supplies all the flavour and what little texture there is, and a chewy crust would have nothing in the filling to chew against. Made right, the sandwich is ham rounded out and lifted; overdone, it is bread and sweet brown sauce with the ham lost in the middle.
The variations are the rest of the sharpened-ham family, each named for its cutting agent. Ham and piccalilli swaps the sweet-sour for hot mustard and a crunchier vegetable; ham and mustard strips it back to heat alone; ham and tomato reaches for moisture rather than acid. Within the pickle itself, the small-cut smooth versions and the chunkier original behave the same way against ham at different scales of texture. Each deserves its own article rather than being crowded in here.