Hi George, you are quite right that you have just left the lettuce too long before harvesting and it is now bolting. Lettuce just doesn't stand well in the ground once the plants are ready - you have about one week to harvest them before the plants start to bolt. The leaves will start tasting bitter but here is a recipe for lettuce soup that will use some. Apparently you can soak the bitter leaves in water for a few minutes which is supposed to remove the bitterness - but I've never tried that.
Great British Cookbook - Lettuce Soup