I've known an ex Nottinghamshire onion growing (now retired) champ since childhood and bumped into him today. Remembering your comments about an ambition to grow a 3lb specimen I asked a few questions and there seems no reason why this could not be achieved quite easily as long as basic care and procedures are followed. There will be no need for heat lamps or light bulbs to be used ........ just basic regular feeding with planting in a good soil and soot mix starting mid April. Pete has some small plants grown from his own seeds and if interested will let you have half a dozen for £2.50 when they are ready. He used to show (and win) near you at the Moorgreen show but no longer.
If interested I'll post his number and you can arrange to meet at his allotment which is in Southwell. Mind you, although a retired plumber, a lifelong 'Pie and a rough owd country boy ......... don't talk politics or mention Forest!