Our good pal here, DD, (Digger Dave), has a fool-proof method for leeks which I now use with great results!
Sow them a bit earlier (like now), in a seed tray, wait until you can transplant the biro-refill size seedlings in a deep box, like a cat litter tray with drainage holes, with a bit of space for each leek then stand back!
Dibble and feed the hole as Mum says, and feed every week with comfrey and nettle tea if you have it, and keep watering if it's dry everywhere.
Plenty of old manure on the bed the year before is a good move, but that may be too late for your crop this year! And if you want a late leek, like we do here, just check the seeds to make sure they'll stand the winter and get into March - they should do!
Best of luck anyway, leeks are such a rewarding crop, and are such a welcome veg during the winter months