some research findings

I've been doing some digging around and found out some interesting stuff.
http://asap.sustainability.uiuc.edu/members/dananderson/documents/org-prod/
Bill Liebhardt, 2001. OFRF Information Bulletin, Summer 2001, #10.
This report found that the assumprion that organic crop yields would necessarily be much lower than intensively grown crops isn't the case. Yields in some crops were lower, but only by around 5%. He said "for a total of 154 growing seasons for different crops, grown in different parts of this country on both rain-fed and irrigated land, organic production yielded 95% of crops grown under conventional high-input conditions.”
This doesn't seem so bad. I'm sure that better food disatribution and storage could save the other 5%. Wasting less food would certainly help make up the shortfall.

The BBC website also had some interesting info at http://www.bbc.co.uk/bloom/flash.shtml#/actions/growyourown.shtml
I've copied a chunk of their article in below.
"Research suggests feeding each of us contributes around 1700kg of CO2 a year, but scientists are a long way off pinning down exactly how much of that you'll save by growing-your-own:
You will save the most CO2 by growing foods which have the highest CO2 impact such as Mediterranean-style veg, (courgettes, peppers and aubergines) salads and tomatoes. We eat them all-year-round, out of season, which means they must be grown in energy-demanding heated greenhouses (here or abroad) or flown over. The UK is fairly self-sufficient all year round in carrots and potatoes, so growing these won't save as much CO2, but will save you money
According to one study if you grow 5kg of tomatoes instead of buying them in a UK supermarket (grown in season in the UK), you could save the equivalent of up to 45kg of CO2 and around £20
...Growing your own food reduces food transport on the roads - a quarter of all UK heavy lorries on roads are carrying food between farms, processing units, food storage deports and supermarkets
Climate change projections suggest arable crops will need heavy irrigation in future if they are to survive in the south of the UK, and food crops may be even less secure in some developing countries. Growing your own food is one way to adapt to these changes"

So I've learned that from a climate change point of view, it's best to grow foods that would otherwise need to be imported or grown in heat, such as tomatoes. Well that's fine, but I don't think I'll be able to grow enough to meet my needs through the winter and unless I set up a canning factory or buy a huge freezer, or make an awful lot of chutney (and I can't use chutney in all of my cooking!), how would I store them anyway? To be really strict about this I'd have to stop buying canned tomatoes.

I wonder what difference there is in energy usage between canning and transporting to the UK and producing in the UK on my allotment and then freezing in my freezer. Hmmm...