Hi Jock
Are these Kelsae onion seeds?
If so then you might find the following info from the Mr Fothergill's website helpful.
"When to plant outdoors: December to January
How to grow outdoors: Johnsons Seeds recommend: A medium type soil is preferable where possible. Dig in plenty of well rotted manure during the autumn prior to planting out. Keep the onion bulbs well watered. Apply a top dressing of a good general fertiliser. Harvest: Bulbs are ripe when the leaves turn yellow and the skin begins to peel away. Lift carefully and lay in rows to dry out. Store in a dry, airy place."
Hope this helps.
Grawrc