@Bagpuss But if you have a decent greenhouse, and you use the latest technological offerings that are out there, you can extend the seasons a bit. And then if you produce enough that you can freeze a lot of it for use through the winter. So for example, if you have tonnes of carrots, and beans and stuff, you could make loads of soup. If you store them right a lot of vegetables can be kept for a month or two in the home, and things like leaks and most roots vegetables can be kept into the new year if they are stored in sand and in the normal British climate.
It also depends on what varieties you get and when you plant them. Some brussell sprout varieties can be left till as late as February before being picked. Then you have options with well stored potatoes, and beetroots and carrots for lots of different meals in the winter months. With the right varieties germinated early enough you might start getting new crops in April and May, depending on what it is. I think the thing is that if you are being self sufficient you need to expect to have periods where you be eating a lot of one thing. I've had times when I was a kid where we had all of our vegetables and most of our fruit from a fairly unplanned plot from around May until November. Really it was only the storage that stopped us from living off of it all year around.
And there is also the option of pickling things like cucumbers and onions, making jams and chutneys with berries and fruits, the old traditional ways people used to stretch out the crops into the harder months. Some things take a few years to actually produce useful fruit (like gooseberries, and rhubarb). Some have a very narrow window of harvest so you need to pick them and turn them into jam or something if you do not want to waste them. You soon realise how many airmiles go into keeping strawberries and raspberries on the shelves all year round when you have been living off of your own plot.
Also, don't forget about herbs. They are often more trouble than they are worth trying to grow from seed, so the B and Q plants for a few quid a go can be a good alternative. If you bang some basil and mint, and rosemary in, maybe some thyme, lavender etc. Thats is mate, you've got a lot of flavours and all sorts there.
And if you've got kids, they love it all. My two and half year old nephew has been out there all Summer helping me get all sorts done! "That's mint needs watering Uncle! Can I water the beetroots? Can I pick a carrot please? Look! Look! Its a tomato!!!! You need to put down some grass seed there Uncle, I'll water it and then tap it in." It's great
That is something I tried for the first time this year, and after several planting with different seeds, I got absolutely nothing. It has been a very strange year for me.