Confusing leek

.    Hi, new to growing veg, we had a bag of leeks that got forgotten about and the started to grow in the bag, so planted them. They have sprouted well, and produced a bulb at the top with a spike, is this a bulb I can cut off and plant or will it turn into a flower??? 

Onions can do this sometimes and their flower heads plus stem are nipped off, but if your leeks are doing it now, it sounds as if they are under stress. If you have the space, you can try them, but may not be any good.

Doubt that you'll find many people who have tried this, if only because when bought from a shop they are already fully grown, and that being the case they will quickly run to seed - in theory you could save and sow the seeds next year, but the leeks themselves will probably be inferior to how they were when first bought, especially as they will now have a flower stem running up the middle of them!