I believe the stereotype of bland, overcooked food dates to the early 20th century. In centuries past British food was known as being rather spicy, as it incorporated lots of spices coming from the colonies.

As I understand it, the downfall came with the advent of canned food and industrialization, and was cemented by the deprivations and rationing of WWII and the postwar era.

Today I think it's certainly possible to find excellent food in the UK, although much of it is going to be of the ethnic (Indian, Chinese, other Asian, etc.) variety. While you can get excellent, "traditional" British food (beef, pies, etc.), that probably comes at a higher price point because it caters to, well, older people.

I will say that I absolutely love an English breakfast fry-up.