I think it's very likely that you already have young foxglove plants in the ground which will flower next year, but as Dovefromabove says, broadcasting seed will ensure an ongoing free supply, but the offspring may not come true to the parent plant due to cross pollination. Like Excitable Boy, I relocate some of mine- I'm in the south west too! Incidentally, you can predict with a great deal of certainty what colour the flowers will be by looking at the base of the leaves. If they have a pink flush (as seen in the main plant in your picture) the flowers will be the usual foxglove pink/purple. If white, the flowers will be as well. I have a variety that come up year after year, all self sown, in a variety of pinks, whites and apricot, as a result of cultivated varieties that I grew yolks ago.