hankyspanky A year ago (with a No Deal Bxt in mind) I started growing a few crops. I have a very small garden, facing north east
which is now mainly wild life welcoming, so not much free space at ground level. I bought three raised frames, biggest only 4ft long, and narrow, but did very well in those with rocket and perpetual spinach.
I also grew radishes and cut and come again lettuce quite thickly (any excuse to avoid thinning out seedlings!) in a couple of old expanded polystyrene boxes and discovered that fresh radish leaves make a lovely crisp addition to salads and I actually preferred those to the actual radish!
I've found from past experience that any old seed from a shop bought tomato will grow successfully. I did buy Sweet Million tomato seeds last year though, and a larger variety, and in the end had sixteen(!!!) healthy plants to plant out in any spare ground. They did well although planted late. Those that didn't ripen off I froze either whole or sliced to use as fried some time.
I also grew some amazing large crisp peashoots indoors in a shallow tray with compost, from a cheap pack of 'Bigga' dried peas from Tesco, placing them about 1" apart from each other - I got about three crops from each sowing.
I read about overwintering kale, and as long as it germinates before the frosts, and it doesn't go below -5' without protection (fleece will do) it should have a head start come spring. I didn't sow mine until the first week in November, which was a month after the recommended time but now have a lot of healthy 'spare' seedlings, and 16 plants doing well and spaced out in the 4ft frame.
You can buy parsley and other herbs from supermarkets and repot and even split them further - parsley and mint and chives do well that way.
I live on my own and have a few mobility and visual problems and maybe my plans woudn't suit anyone wanting a bigger yield, but what began as an experiment has fired me to try growing other things this year in addition. I started this because I couldn't bear the thought that fresh veg might become unavailable, and had the added bonus of amazing flavours and a healthy new interest. And I learned to be more relaxed about the whole thing than I was when I began... it's very therapeutic.
For anyone who wants to experiment but thinks they lack space and experience, I'd say just go for it - there's loads of info on the internet about gardening in small and awkward spaces.
Just keep in mind that if you want your plants to feed you, you have to feed them first 