You can go ahead and count on any interesting study the Guardian references it's not going to cite a source for. It's a real shame considering I usually enjoy their articles for their often unique coverage and just amount of depth to make me want to read more, but no links are to be found.

Also, I find almonds and pistacchios somewhat filling, as well as oatmeal bars. If I need more protein during the day, I bring a casein shake to work with half skim milk/water. They'll hold off hunger for a while as well, much better than whey.