The New York Times has a quirky little article about 'affordable' things to do in London.
A good rule of thumb is "if it costs a dollar in New York, it costs a pound in London" (though, of course, there are nearly two dollars in a pound). In fact, perhaps the best advice of all is: Don't do the math while spending pounds; it will only make you queasy. Nonetheless, you can still ferret out a few bargains.
And they have some strange suggestions. Apparently, the Berkeley Hotel is the place to go for bargain food, at just £30 per person for lunch or £80 for dinner. Hmmm, doesn't seem to be listed in our copy of Time Out Cheap Eats.
Otherwise, the article runs through the usual obvious choices, such as our wonderful museums, which are free 'thanks to the British government's largess'. (Or John Prescott, as we call him.)
If you're looking for good, cheap things to do in London, ignore the article itself and look at the many useful reader-comments.