Roughly chop the basic vegetables (carrots, onion, leeks, celery), as well as any similar vegetables you intend to use.
Place into a large non-stick soup/stock pan and begin to "sweat" for ten minutes on a medium-low heat, stir to avoid burning or sticking.
(You may add a table-spoon or two of olive oil or similar if you like, but it isn't necessary).
When the vegetables have reduced in volume and have begun to cook, drain and add the tinned beans, also add the tins of tomatoes, the pearl barley, salt & peppers.
Add any chopped fresh vegetables you wish to use (e.g. runner beans).
Add enough boiling water (from a kettle) to cover the food by two or three inches. It should feel very liquid - the pearl barley will expand and soak water.
Raise heat to start a boil, then reduce to a strong simmer. Stir well and frequently to avoid sticking, add water if it's becoming too thick.
Simmer for about 40 minutes. The pearl barley should have expanded and be cooked, the liquid reduced.
If it is too watery, cook a little longer; if it is too thick add some boiling water.