You absolutely MUST succeed with leeks, living where you do! I note you are restricted to planting boxes though. Sow the seeds early in spring in good compost in a short row. I found in two short rows about two feet in total, I had well over a hundred leek plants when I transplanted them.
Leeks are very slow to germinate and grow at first and need a lot of moisture. They look just like onion seedlings when they first come through so shouldn't be confused with most weeds which have broad leaves. Don't bother to thin them but just let them grow on in the same part of the box until June.
By then, a lot of them should be the size of large pencils or a bit smaller. You should be able to pull them out or dig them out easily with a hand fork.
In another box, make a hole for each one with a dibber. (A pointed stick the size of a fork or spade handle.) I plant mine at a spacing of nine per square foot (3 sets of 3) as this makes fairly small leeks which we prefer. For larger leeks you need greater spacing. Although your boxes are only two feet deep, this should be enough, and if you dib a hole about six inches deep, just drop the leek seedling into this.
Then carefully fill the planting hole with water.
By making a hole for each leek like this you increase the amount of blanched white stem you get and it allows the leek to expand to fill the hole, which gradually fills with earth as you water each week.
Some people say you should trim the roots and cut the tops of each leek seedling, but I never do this and have never had problems.
Keep your leeks well watered until they are established, and you should get some good crops by winter.

thankyou bertiefox ,yes living just outside cardiff i should be able to grow leeks , daffodills i have no problems with ,hopefully sometime this year i will put a photo on my page of them,lia.