Pea soups and pease pudding have long been staples of the British kitchen, filling and cheap, with dried peas keeping well over the winter well before the days of frozen foods.
A London Particular is a particularly thick pea soup named after the dreadful fogs that enveloped London from the start of the Industrial Revolution to relatively modern times: "This is a London particular", I had never heard of such a term. "A fog, miss" said the young gentleman (Bleak House by Charles Dickens ). But whereas the fogs killed thousands, the simple but nourishing pea soup kept more alive.
Ideally the soup should be made with the stock from a smoked ham or gammon hock, and to be at its most authentic should use yellow split peas to mimic the foul air that blanketed the London of Dickens' day, and later in the same century hid some of Jack the Ripper's handiwork. The smoke from coal fires, the railways, and London's industries mixed with the natural fog rolling in from the Thames estuary to create the capital's killer smog.
If you don't have yellow split peas, green will do fine.
The other ingredients are usually an onion or two and a carrot, perhaps a celery stalk and a few celery leaves for a bit of extra flavour. The peas are simmered in the stock until very soft, the other vegetables can be cooked in a little oil or butter, or simply added to the peas and stock to simmer. In Dickens' Day there were no food processors (beyond the kitchen staff of those who could afford them), but such a device makes it easier to zap the cooked mixture until it is of a nice smooth and stand-your-spoon-up consistency.
With being made from a ham or gammon hock it is likely that the soup will be on the salty side - do check the stock before use, and correct over-saltiness with more water or cooking a potato in it before use with the peas.
Adding garlic is not really appropriate, but it would not harm the flavour, and a bay-leaf is a nice addition too. With a hunk of bread this dish is hearty enough to serve as supper on its own, as it would have done for many of those who ate it in Victorian times. Chopping the meat from the hock and adding that after the soup has been liquidized makes it better still.