Let your leek set seed
When the pointy cap falls off and the leek flower is out, take a pair of secateurs and give it a haircut
Steps shown in picture form
What happens is that the leek will throw out little bulbils which you can use the same way that we use onion sets for leeks next spring
Hat nearly off
Hat off and flowers set free
Start shaving those flowers off
Scalped. The bulbils will grow from the bottom of the flower stems and the remaining stems will die back. Pics of the bulbils to follow...