Shuttle-Lunch
London moves fast. This includes lunch. A large chunk of workers eat at the desk, and so need quick choices, quick food, quick variations. The good news is blow-in's also get to enjoy the choices.
Pret-a-Manger
All the sandwiches! Are they everywhere? Yes. Are there options other than sandwiches? Yes. Will it change your life after 2 bites? No. But it’s still a decent choice of sandwiches, always fresh, if probably a bit overpriced. Always a good fall back if stuck.
Itsu
Sushi / Asian food. Again, part of the Pret group, food is always edible (sushi, salads, etc) . They do a nice selection of hot-pot type food too (noodles, rice bowls). Also, like Pret, they are everywhere.
Leon
Great shout for healthy food. Nice mix of hot food (chilli, veggie breakfast fry, rice box). Smallish portions, but more than enough for lunch.
Crush/Pure/Chop’d/Tossed
Healthy, healthy, healthy! These are quite close in menu choices, lots of veggie/healthy/salad options. They do pretty decent fresh juices and nice mix of healthy rice boxes/hummus/interesting salads. Chopped in particular does pretty huge salads (like head sized salads).
EAT.
Not as good as Pret, but edible. They do good hot-pots and good basic sandwiches (ham and cheese, chicken and stuffing). Exciting as it sounds, it’s better than other places.