when you say your plot is not registered, do you mean that it is not registered to you, or that it is not registered as part of the allotment site?
According to the government land registry, that particular plot is unregistered - this private allotment site dates back to 1910, many of the original owners have died, and many of the plots are now unregistered to any title owner.
Either way I would be careful about erecting any kind of expensive building with permanent foundations, even if it were permitted. What happens if you are turned off your unnregistered plot?
Well, as the plot is unregistered, and as, due to access problems, the land cannot be bought by a large development company and built on, it is highly unlikely that we will be turned off. Ultimately there will be far more man hours invested into tending the plot than financial input. We're hoping this structure won't be expensive; the idea is to use salvaged, recycled and reclaimed materials, which may not be possible with a log cabin of course! The log cabin idea is only the starting point of an idea...
If your plot is not registered as part of the allotment
Yes, it is part of the allotment site, just that particular plot is unregistered.
depending on what the current use of the land is registered as.
It is designated allotment land.
Also if it is a private site - what does your landlord and lease have to say about a permanent building? I think the Allotments Act applies to Local Authority sites, private landlords make their own rules.
There is no private landlord or lease for the part of the allotment on which we plan to erect a structure, although we wouldn't want to do anything which the old timers on there weren't happy about. Their greatest wish is to see the allotments come to life again after 20 or so years of utter neglect.