Working class food was very plain, as in the 19th century around 25% of the population lived below the poverty line. Most families lived in one-room tenements, so all of their food had to be cooked over the fire as most of them didn't have ovens. I found a couple of paragraphs on one website that deals with working class food staples - I know that basically they made the best of what they had:
"In the early 19th century the working class lived on plain food such as bread, butter, potatoes and bacon.
Butcher's meat was a luxury. However things greatly improved in the late 19th century. Railways and steamships made it possible to import cheap grain from North America so bread became cheaper. Refrigeration made it possible to import cheap meat from Argentina and Australia. Consumption of sugar also increased. By the end of the 19th century most people (not all) were eating much better food.
The first fish and chip shops in Britain opened in the 1860s. By the late 19th century they were common in towns and cities.
In the late 19th century the first convenience food in tins and jars went on sale. Although the principle of canning was invented at the end of the 18th century tinned food first became widely available in the 1880s. Furthermore in the 1870s margarine, a cheap substitute for butter, was invented. Tomato ketchup was invented in 1874.
Several new biscuits were invented in the 19th century including the Garibaldi (1861), the cream cracker (1885) and the Digestive (1892). Furthermore new sweets were invented during the 19th century including peanut brittle (1890) and liquorice allsorts (1899).
For centuries people drank chocolate but the first chocolate bar was made in 1847. Milk chocolate was invented in 1875."
If you're focusing more on the Regency period then only the first part of that will really be relevant - look up the Poor Laws, and see if you can find anything about what kind of food was served in the workhouses - that would probably give you some idea of what the working class generally ate - mostly one-pot meals, I think, because of the cooking over the fire issue.
As for the nobility, there was a huge gulf between them and the working class, I found a link to a
Regency Cookery course that gives some good examples of the meals eaten by the well-to-do, lots of meat, including game, and rich desserts.
Here is another page with a list of main dish recipes that would have been served at the tables of the rich folk, including a 'broth for the poor' to 'feed a multitude', which the poor wouldn't have been able to afford to make, because it includes beef, which would have been too expensive for them.
Hope this helps!