Thank you Tee Gee :)
All my overwintering onions will be grown from seed this year - it was successful with Japanese varieties last year, so this is the time to experiment and see which varieties overwinter/taste good!
The lovely thing about autumn sown from seed is that if they fail, I can always plant setts in the spring ;) Thank you for your interest and advice on numbers, will let you know how we get on - and in the light of your comments about early warmth, I might sow half earlier and plant the seedlings around mid-August ::)