Ok, I think I understand your question now, thank you for clarifying. I'll give you the best answer I can. Some of this change happened during the rationing during the world wars and post-war. I'm not going to get into that as it's more modern than I research.

We're going to start in 1600.

Actually we're going to start in 1597 and 1604.

"The second part of the good hus-wiues iewell" was published in 1597 in England and contains recipes where food is roasted, boiled, stewed, baked in a pie, and jellied. There's lots of use of spices such as ginger, pepper, cinnamon, and sugar various sauces to go with them and the use of verjuice (unripe grape juice).

"Ouverture de Cuisine" was published in 1604 in France and includes recipes where food is roasted, boiled, stewed, baked in a pie, and jellied. There's lots of use of spices such as ginger, pepper, cinnamon, and sugar various sauces to go with them and the use of verjuice (unripe grape juice).

Now the recipes aren't the same, there is regional variation between them but the cooking methods and concepts are similar.

Now we're going to move forward in time to 1651. François Pierre de la Varenne published "Le cuisinier françois". This book marked a change in French cuisine which lead to Haute cuisine. Before this there were differences between courtly food and plain food but it had more to do with amount and cost of ingredients rather than cooking methods (Mennell, Stephen. All Manners of Food: Eating and Taste in England and France from the Middle Ages to the Present. Chicago: University of Illinois Press, 1996.).

Part of it was the concept of (and I hate myself for bringing this up) conspicuous consumption. I'm of the opinion (and there's big arguments over this) that it wasn't the be all and end all of cuisine in the Renaissance, but it's definitely a concept. The use of one food item over another because it was more expensive or the use of excessive spices first because it tasted good (they loved spicy dishes in 16th century England almost as much as they loved sweet dishes) but also, to a lesser extent, because it showed off wealth that you could afford to use, for example, two ounces of pepper in a dish, or could afford galangal instead of ginger.

Back to the 17th century. "Le cuisinier françois" was translated into English in 1653 but it didn't change cooking in England the way it did in France. In 1668 "The Closet of Sir Kenelm Digby Knight Opened" was published and although it very much contains changes from the 16th century it's still using similar concepts.

By the 18th century French cooking was considered the height of cooking in England (Mennell 89) among the nobility, but the adoption of French cuisine took time. In the late 16th century and early 17th century the "courtly" food being developed in Italy and France hadn't yet come over to England (Mennell 85) as it was considered too pretentious and against the nationalistic sentiments in England; the major English cookery books of the time, even after the translation of Le cuisinier françois, ignored their French counterparts (89). It wasn't until the Restoration of the Monarchy that the "courtly genre" of cookery books began to appear in England (ibid.). These books, based on French model, still took until the 18th century before they were more than simply a courtly version of the English style (93).

There was, however, a push-back against it as the English were very Nationalistic. So you had two different types of cookery happening in England in the 18th and 19th century. One was food which still had some holdovers from Medieval and Renaissance cooking and was now considered essentially middle class or commoners food, while the other was an English take on French cuisine (see William Verral's "A Complete System of Cookery") which was primarily for the nobility, gentry, and their emulators. These two cookery styles continue through the 19th century.

So as you see the idea of a unified "British" cuisine is a 20th century concept, and in England they unified under the common food rather than the courtly food as they did in France. However as to why one and not the other you'll need a culinary scholar focused on the 20th century.

I hope that helps.

Although I'm not a food historian, I am an economic historian. And the two things aren't as disconnected as you might think.

Prior to the industrial revolution, the British Isles were sparsely populated, and agriculturally unproductive. This not only created a situation where wages in England were relatively higher than the rest of Europe but also incentivizing producers to make their expensive workers as productive as possible in order to compensate. In short; poor English agriculture (and, as a consequence, food) helped set the stage for the industrial revolution.

Italy, on the other hand, was incredibly agriculturally productive. The ancient Romans believed that the goddess of agriculture, Ceres, lived in Sicily; not unsurprisingly one of Italy's most culinarily diverse regions along with Campania, where the volcanic soil is absurdly fertile. Northern Italy too is perfect for the growth of rice and grain; while the peninsula's position in the center of the Mediterranean made it a natural point of exchange, and this enhanced the local food culture. This had a measurable impact on Italian economic history; with Italian entrepreneurs not only seeing no reason to industrialize well into the 19th century, but allowing the peninsula to sustain the existence of many fragmented independent states. In fact, nearly all scholarship on Southern Italian economic development agrees that the capitalist class in the Kingdom of the Two Sicilies was heavily biased towards acquiring more agricultural possessions, rather than rendering their existing possessions more lucrative, or finding other enterprises to invest in; there just wasn't any point.

France and Spain were in a similar situation; perhaps Iberia was less fertile than Italy, stabilizing to support three polities instead of the dozen Italian ones, while France's political-economic development was characterized by a long and arduous trek towards a unitary monarchy, with a multitude of regional political actors. In fact, high-fertility regions in France coincide with those regions which gave the French monarchy the most trouble: Burgundy and Aquitaine. In England, no similar regional political dynamics emerged; English unity, coupled with French dis-unity, was a major characteristic of the hundreds years war (and I'd argue is a similar dynamic to the one the German Kaiser had in Italy three hundred years prior!).

Now, modern "Restaurant Culture" emerged in France in the late 19th century, which is why Western Culture perceives French food as "Fanciest," followed by Italian and other mediterranean foods. I even asked a question with regards to the development of the French restaurant on this sub, but unfortunately didn't get any answers! In any case, I hope my answer will have helped you understand that cuisine diversity and flavor is a function of what products local cooks have at their disposal; and in England, they unfortunately didn't have much compared to the Mediterranean!

Are you able to clarify your question a bit? Perhaps what time period you were hoping for. I assume you mean 19th and 20th century, but the answer is going to depend on when you want to know about.