This is a question with a really, really wide scope that I think would be more likely to get a direct answer if you could specify a certain subject or angle on the show where you're wondering about accuracy. However, I do have a few past answers that speak to this issue:

On Downton Abbey, married women have breakfast in bed and unmarried women go downstairs and have it. Did this really happen in the early 1900s? Why?

What were rich British parties like in the late 19th and early 20th century?

What did landed people do all day?