Electric Kettles: Why wait for the water to boil? Just plug in the kettle and get your hot water fast and efficiently. I use mine all the time for cooking, and less often for tea. I can't believe I had to go overseas to learn this; they are only a few dollars in "big box" stores.
Salted Lemons: They are called "Preserved Lemons" or pickled lemons in the US, I can find them in my African section of the local grocery or at the near-by Middle-Eastern grocery but you can also buy them on-line. One lemon diced fine adds a wonderful flavor to cous-cous, salad and numerous other dishes. Part pickle, part fruit -- it has endless uses.
Love the Lamb: I was a "lamb hater" until I stayed with some beautiful cooks in Manchester. They served a roasted lamb that was so delicious. And you truly have not tasted Shepherd's Pie until you have it with freshly ground lamb.
A Good Curry: The English love their curries. It was quite surprising to me as I had stereotyped the English as bland-eaters. Their love of the slow-heat is inspiring and I have tried quite a few more curries as a result of my British buds.
Fish Pie: I know, it sounds awful. It is like shepherd's pie but with the addition of boiled eggs (yes, really) and spinach. I first tried it based on a recipe by the British chef Jamie Oliver but a friend visiting from England last year revolutionized it for us. He added Chorizo to the mix and our love of the fantastic fish pie was realized.
Fish makes me think of Fish and Chips. I am not a fan of pub food, mostly, but I do like The Ploughmans. It was actually the inspiration for "the snack plate" I make for our Littles. It's lighter and fruitier than a Ploughman's, and I cut everything bite sized, but it is their absolute favorite.
So maybe that's really 6 things.
There is always time for tea. Tea in England taught me to slow my pace and sit down and savor the day -- before jumping up and resuming my normal dashing around! :)
So what are your "borrowed from the Brits" favorites?