I might sound it, but i'm honestly not jokin here. Think of how far the allotments are away from you, now use that distance as a radius around your home, i bet there is a strip of neglected land perfect for the job within that distance. Go and clear it. Dig it over, enjoy the random shit you pull out haha, and get gardening. Later, quietly erect a modest shed and maybe a chicken coop.
I am certain NO-ONE will complain. If they do, so what? Cause no harm, injury or loss, and you are completely within the law and whats more, you'd be living your dream! Nothing to lose!
The worlds a marvelou