I am a tip group editor for London and whilst grouping the restaurant tips I came upon one for Thai Silk restaurant (a decent place), which used to be directly opposite the side / back door of Waterloo Station. This tip dates from 2007. I am in that area frequently, and I know that this restaurant has moved some time ago, about a ten minute walk (despite what the website says) from it's previous location. I offer this tip merely to assist travellers who may go looking and find a different restaurant from the one they were looking for.
Super Thai restaurant and bar, which becomes very busy after office hours.
Nice surroundings and a set lunch menu with a choice from a selection of three dishes for starters and mains, costs £5.95. Light and healthy and certainly a substancial meal.