I love most things British, from Monty Python to Pride and Prejudice, so Downton Abbey is right up my alley. I'm loving the premiere episode so far, especially because it reminds me of some books that I also love.
One of my favorite authors, Kate Morton, wrote a great book called The House at Riverton, which focuses on an upstairs/downstairs story set before and after World War I. Ethel the maid in Downton Abbey talked in the premiere about the world changing because of the war, which certainly affected everyone, but especially changed the life of people in service. The House at Riverton is a mystery and a family drama rolled together. It was fantastic and I can't recommend it enough!
My second recommendation is Jacqueline Winspear's Maisie Dobbs series. These are mysteries set after WWI, which focuses on the generation that survived the horrors of the war. Maisie was in service herself, but was a nurse during the war and after begins a detective agency. There's one book that centers on the white feathers that the women handed out during the war to any men not in uniform, which happened in the Downton Abbey premiere. I enjoyed the first few Maisie Dobbs' books a lot but never finished the series, although my mom still reads the books regularly and loves them.
Finally, A.S. Byatt's The Children's Book takes place in the years leading up to WWI. It features a Bohemian family living in England. The mother write's children's novels and the plot revolves around the various children, as well as the artistic types that fill their world, from Oscar Wilde to German puppeteers. It's a hefty book and I definitely read it with my phone opened to wikipedia to read about all the historical figures, but it was worth it!
I saw a lot of Brendan Coyle, who plays Bates in Downton Abbey, over the summer in another series called Lark Rise to Candleford. It also takes place in England, but earlier in history and features a lot of regular British actors that show up in a lot of the BBC productions, like Julia Sawala, from Absolutely Fabulous (which also premiered last night). It's about a young girl named Laura who moves from the tiny, poor hamlet of Lark Rise to the town of Candleford where she works in the post office with her cousin, Dorcas. I actually read about this series in an interview with Modern Family star Ty Burrell, who loved it. I've only seen the first three seasons (out of four), but Brendan Coyle is great (and infuriating sometimes) as the father of the family. If you like that show, also check out Cranford, starring the fabulous Judy Dench and featuring Michelle Dockery in the last season, who plays Lady Mary in Downton Abbey.
Happy reading and watching!