I was thinking of clearing out some old seeds, but wondered if it wasn't
worth just giving them a last chance to sprout in some compost in my
(unheated) green house. Questions:

What chance have two year old parsnips and leeks of sprouting?

Is there a size above which it becomes infeasible to transplant parsnip
seedlings? (I once read that you shouldn't be able to transplant root
vergetable seedlings, but I managed okay this year with swedes and beetroot)

Will seeds planted this early 'get ahead of themselves' and tend to go to
seed?

Tim Lund, SE London, clay based soil