I bought Carling peas online. They came with a recipe, of which the following is an adaptation:

CARLING (parching, black, pigeon, maple) PEAS, as used for traditional Lancashire Bonfire Black Peas

1 cup / 150g peas soaked in water for 24 hours
After soaking and draining the black peas, cover them in plenty of salted water in a large pot, and bring to a raging boil. Then turn down the heat to a rolling boil, cover the pan, and boil for about an hour or slightly longer until they are very well-cooked, with the skins coming off. Once the peas are cooked and soft, drain them.
Now:
1. Put 250ml / 1 cup of cold, fresh water in a pan, add the peas and bring the water to the boil. Turn the heat down to a high simmer.
2. Add 1 teaspoon of vegetable stock / bouillon powder to the peas and also 2 teaspoons of cider vinegar, as well as some salt and freshly ground black pepper.
3. Allow the peas to stay on a high simmer for about 10 minutes, stirring frequently.
(The peas are ready when there is a small amount of grey-black liquid in the pan, just enough for the peas to be moist but not lots of liquid left.)
4. Serve the peas individually in small pots, and season with salt and vinegar to taste.