Q.Growing tulips from seed.
Last autumn, we bought six tulip bulbs and planted them in the garden. As spring progressed, these grew and flowered, a very dark red almost black flower. After flowering was complete, we left the plants to die back as usual, but one did not. Rather, it developed a large seed pod which we allowed to develop until it dried. We now have the pod with a whole host of seeds. Is it worth planting these, any ideas what would happen? If we should go ahead, when shoud we plant?

Intruiging, I'll definitely plant them. Can they go in now or should I wait until spring?

It will take 4-6 years before seed-sown plants reach blooming size. The plants will not be the same as the ones you have since you probably have hybrid tulips. Tulip bulbs also form bulblets or off-shoots from the main bulb. Bulblets produce tulips the same color as the parent plant and reach blooming size in the second year. You'll get more bulblets if you don't let a flower go to seed. Here are two articles on propagating bulbs. https://www.rhs.org.uk/advice/profile?PID=101
https://www.gardeningknowhow.com/ornamental/bulbs/bgen/propagate-flower-bulbs.htm