Essentially none. There were laws about adulteration of various food products, but the overall principle was simply "buyer beware." Only in 1860--after a major expose in The Lancet and multiple Parliamentary investigations--was a comprehensive Adulteration Act passed. This act was permissive, however, allowing but not requiring local government bodies to test foods for adulterants. It proved totally ineffective, and was replaced in 1875 with an act that required such testing. Within ten years the purity of food was substantially better, and adulteration was gone completely from many foods by the early 1900s. The standard work on the history of adulteration in Britain in the nineteenth century is Michael French and Jim Phillips, Cheated Not Poisoned?: Food Adulteration in the United Kingdom, 1875-1938

In terms of the space of the restaurant and its standards for cleanliness, I do not know specifically, but it cannot have been too different from bakeries, one of the subjects of my research. It was only after 1863, in the context of adulteration scandals, that bakeries came under surveillance for their health characteristics in relation to consumers. Health officers had looked at bakeries (and presumably other food-production facilities) before that, but only in relation to the workers' health. And, while it was clear that they were unhealthy for the workers, there was no meaningful surveillance and regulation. Even after 1863, some regulations were put in place, but there was little actual surveillance. There are plenty of complaints about the conditions of food production through the rest of the century, but I know of no major inquiries or reforms.

Finally, I should note that the Sanitary Movement was a major part of the urban political landscape in nineteenth century Britain. "Sanitation" at this time, however, was deeply class-inflected. It was, according to Michael Worboys Christopher Hamlin in Public Health and Social Justice in the Age of Chadwick, a means of cleansing Victorian cities of their filth, both in the form of human fecal matter and the activity of working class Britons. Drains, water provision, and sewers were seen as a way to clean up cities from the problems generated by industrialization without raising wages. Sanitary reformers typically focused on things that could be washed away and on poor people. Regulating businesses was never their main priority, and took the forms I mentioned above.

So, if you're a restaurant owner in 1850, you can do pretty much as you like.