Or make your own with low cost bins purchased through the cambridge city council
Or make your own bin as well from old wooden palettes. (One of us got free materials from a builders merchant which is a great way to recycle packaging.)
Many plants prefer rainwater to tap water (especially in our hard water area).If you don't have water butt already, you might like to consider repurposing a small black wheelie bin. As of July 31st, "21 small 120L bins are available. The fronts are painted white so they can be recognised as no longer in use for domestic collection. Offer applies only to Cambridge City residents and while stocks last." Contact
Real Seeds is an excellent source of good vegetable seed varieties - no hybrids.
Or come to our annual Seedy Sunday in January to swap seed and buy heritage seed
Delfland Nurseries Limited sell organic vegetable plants, and can send them out by post (mail order catalog here; they are relatively local (based in March). Plug plants start from 7p each, and allotment groups can purchase plants by the tray at reduced prices.
and if you don't like to see land going to waste, you might be interested in
Cambridge Guerrilla Gardeners
They have been in the local news recently - here is the Cambridge News article (Transition Cambridge does not endorse any illegal activity - please be careful).
Or if that sounds like too much work you might like to try foraging instead