Hello, I don't have an allottment, but is this a peroid of consultation before the new commitee takes over? Or has it happened already? It seems very strange to me that if you have an existing agreement/contract with the council that this can be changed with out due proper consultation with other plot holders who are going to be directly affected not only on a practical level but on a finacial one as well. If you have any paperwork/contract of when you took over the plot that will certainly strengthen any arguement that you may wish to bring. Even if it's not that detailed- the longer the contract you have, will be in your favour.
I agree- there is strength in numbers- maybe get some consensus of opinion from other plot holders. It really depends on how much time & energy you want to devote to this. Sympathatic to the cause town/local/county councillors maybe able to help as well.