i understand allotments where for own use and not for resale or profit?
It is certainly the case that most councils have a bit in their tenancy agreements to cover this. Ours say quite clearly that selling produce is not allowed. If it is a private site, things may vary, but if your landlord says no, then that is it.
We do a lot of swapsies on our site and the council asks for donations of produce for a big town meal they lay on (or used to pre-Covid). I also give stuff to neighbours at home, newbies struggling to get plots into any sort of condition to grow anything or even the odd passer-by who asks nicely. I’m sure my rhubarb patch is visible from space so I give plenty of that away. It is a triffid I inherited with the plot and grows so madly it is only the extra picking that keeps it in any sort of order