I would have thought a kitchen window sill too warm for leek seedlings.

Thanks for answering, should I move them somewhere cooler or are they beyond help?

My onions did the same I had left them in my heated propagator too long so I have had to sow some more.

I agree with Steve sow some more but you can also try moving the ones you already have somewhere cooler.

But if they started drooping at one end of the tray and the droop started spreading they need watering with copper sulphate solution - Cheshunt compound if you can still get it.

Thanks all, I've sown a load more now outside in my raised bed with fleece protection so I'll see how these get on.