I'd agree with Munty, (we have to on here otherwise he'd unleash the hounds). I was going well digging Mr's Digger's plot, but have put everything on hold until next week, firstly because of the cold, now rain is forecast Thursday & Friday!
I've you really want to do something, how about starting your leek & onion seed in seed trays, this is how I do it, from a previous post.....
Now this might seem a bit painstaking, but I find it well worth the effort......
As I use cat litter trays, as they are nice & deep,be sure to make holes in the bottom though - a hot skewer will do the job. I use compost from grow bags, as it seems one of the cheaper ways to buy it.
You could also start you sprouts off. I put one seed per plant plug seed tray insert, and then pot on into 3" pots when large enough.
Now here's the painstaking bit, I plant the seed individually 1" apart 1/2 deep. That way they don't crowd each other out. I get nearly 100% germination in the green house. One of these trays will produce 96 plants. Compost has to be kept moist. When a reasonable size they can be moved outside to grow on. I then transplant when they are the thickness of a pencil.
It's something I read somewhere, I didn't make it up my self, but when they go in they are real sturdy plants with no previous thiniing or transplanting needed
You could also start your sprouts off, I use seed tray inserts, such as the one here, (illustration purposes only!)..
http://cgi.ebay.co.uk/Plant-Cell-20-Cell-Seed-Tray-Insert-case-pack-of-10_W0QQitemZ180096851389QQcategoryZ20515QQssPageNameZWDVWQQrdZ1QQcmdZViewItemOne seed to a cell, 20 seeds to a half seed tray, obviously 40 to a full one. Place in UNHEATED greenhouse, cold frame or similar - don't want them to get drawn. Keep moist. I get near to 100% germination. When the plant is large enough - say 2" high - re-pot into 3" pots, grow on & plant out.