A book of food history i read argued that it was the British period of isolation in the Napoleonic wars that largely set the trend (and then WWII rationing did their cuisine no favours by homogenising everything in the name of central distribution and standardisation so a lot of local specialties like cheese varieties were lost or nearly so, and a generation of kids grew up with very limited experience of food that wasn't monotonous and bland, and tended to dislike strong or piquant flavours in later life as a result)
Particularly during the Napoleonic era, you have this very localist movement, not just in food. You have the picturesque movement in art, for instance, as British travellers can no longer travel to the great cities of Europe and instead look around their own country for bucolic scenery to enjoy. Wartime patriotism mixed with necessity. Fashion goes the same way - rather than following Paris fashions, English dress starts to branch out on its own. Men's clothing in particular - while breeches were still the thing in Europe, trousers were popularised as elegant mens' clothing in this period by Beau Brummell, who moved in the Prince of Wales' social circles (although in a turnabout, the Prince himself is held in disdain for his over-gaudy taste in an culture where restraint was held as a virtue). And it was the same with food. Things like onions, garlic, chilli, tomatoes, olives etc were much harder to get hold of as they grew better in the warmer European countries. But in general (although conspicuously not in the Regent's household), there was a reaction against (what was seen as) frou-frou fiddly French-style cooking in favour of (what was seen as) good honest simple no-nonsense English food - with much less embellishment. You can even see a touch of this attitude in Austen - there's a scene in Pride and Prejudice where Elizabeth Bennet meets a man who is stated to be indolent and self-indulgent - and Austen demonstrates this by showing him turning up his nose at Elizabeth when she claims to prefer a (virtuously?) plain dish instead of a (dubiously foreign?) ragout.
I'm sure they still did a bunch with herbs - parsley sage rosemary and thyme - and marjoram, dill, etc - and pepper to a degree. But most spices seemed to have ended up in dessert dishes along with the vast amount of sugar from the Caribbean colonies - ginger snaps, cinnamon rolls, allspice in puddings and so on