The original ham-sandwich

I've been reading Henry Mayhew's London Labour and the London Poor which was compiled from a series of articles written by the journalist in the 1840s mostly for the Morning Chronicle newspaper. Although it's slightly after the Regency period, there is a wealth of information useful for anyone writing Regency London and Mayhew interviews many people and comments on how, for example, street trades have changed in recent past.

For example, the vending of ham-sandwiches, which I am guessing, if Mayhew is correct, commenced in the 1830s:

The ham-sandwich-seller carries his sandwiches on a tray or flat basket, covered with a clean white cloth; he also wears a white apron, and white sleeves. His usual stand is at the doors of the theatres.
The trade was unknown until eleven years ago, when a man who had been unsuccessful in keeping a coffee-shop in Westminster, found it necessary to look out for some mode of living,and he hit upon the plan of vending sand-wiches, precisely in the present style, at the theatre doors. The attempt was successful; the man soon took 10s. a night, half of which was profit. He "attended" both the great theatres,and was "doing well;" but at five or six weeks' end, competitors appeared in the field, and in-creased rapidly, and so his sale was affected, people being regardless of his urging that he "was the original ham-sandwich."
Henry Mayhew, London Labour and the London Poor