Unless you were rich, until well into the 19th century, and well beyond that for the poorest people, diet in the UK would have been dull, dull, dull, especially at this time of year when nothing fresh was easily available. Vegetables would have been restricted to what could be grown in the UK and kept over the winter months, but not of course in refrigerated conditions, frozen, tinned or dehydrated, so after months in a dark shed they'd have been wrinkled and tired and some would have been nibbled by vermin. Cabbages and other brassicas; carrots, turnips, swede etc; no potatoes until Europeans colonised the Americas; dried peas, lentils and beans.
Other food: not much fruit outside the summer months. Small wrinkly wormy apples perhaps. In the winter months salt meat and fish, but probably not every day. Maybe some nuts secreted away in the autumn. Old dry cheese.
Lots and lots of bread, because it was cheap.
Milk spoils very easily if it can't be refrigerated and before Louis Pasteur nobody knew how to preserve it with heat treatment. It was often contaminated so adults wouldn't have drunk it except on farms fresh from the cow.
No tea, no coffee, no sugar until the slave trade made it cheap, next to nothing in the way of spices for most people because they were imported and expensive.
I'm sure it would do us good as a society to eat simpler, less processed food, but giving up the huge variety of food most of us enjoy now would make most people's lives much, much harder and less pleasant.