http://www.organiclea.org.uk/wp-content/uploads/2010/04/sellingallotmentproduce.pdf
Allotment Gardeners Can Sell their Surplus Crop
There is however, no restriction on the distribution, by sale or otherwise,
of a certain proportion of the plotholder’s crop. Geoff Stokes, secretary
of the National Society of Allotment & Leisure Gardeners (NSALG) has stated
in a recent article: “there seems to be no justification in preventing
[an allotment] tenant from selling or otherwise disposing of ‘surplus’
produce”3. This view has been approved by Paul Clayden, author of The
Law of Allotments (Fifth Edition), and thus probably the leading specialist
on allotment law!
Of course the definition of ‘surplus’ is a grey area. According to Mick
Marston of the Soil Association, as far as the law, and the government,
are concerned, “limited commercial activity can take place as long as it is
ancillary to the main purpose”4.