My in-laws will be visiting London on their own for a few days at the beginning of May. They are in their early 80's, and my father-in-law is very picky about what he eats (meat and potatoes will do just fine, thank you). They also don't want to spend much (okay, you can stop laughing now...). FIL won't go near most ethnic cuisines - too spicy or full of flavour, or whatever, so unfortunately most of the reasonably priced options that I have found won't work (although FIL will go any place that has salt beef on the menu).
I know where I'd go were I visiting, but that's of no help here. Yes, it's a tall order. They will be staying around Russell Square, will probably be taking the tube most places. Any lunch and dinner suggestions would be most appreciated!