NAS don't "step in" - they are not an arbitration service and they don't "sort things out". Members are entitled to free initial legal advice so if they are members then they are entitled to ask for it - as we have done in the past when we had issues with a member. It is a good service but a limited one but the tenant or member is not also entitled to legal advice - only the site or individual who is a member.
I've been away for a few days so I'm just catching up on the posts. First of all, by suggesting that NAS could give support on sorting this out was not meant to imply that they would sort it out themselves, only that they would give you an opinion on what options may be available to you and as to whether or not the committee may be considered the landlord. Nor was it meant to imply that they would step in and act as the mediator between the plot holder and whoever is defined as the landlord.
Some times the phraseology that you use, whilst it seems right at the time, has different interpretations to individuals so my apologies for the lack of clarity.
Also, I agree with BarriedaleNick regarding the role of the management committee. The committee is there to manage the allotments on behalf of the plot holders. As Johhnyco15 says, this occasionally means that plot holders need to made aware that the cultivation of their plot needs to improve and a process of monitoring whether improvements are taking place needs to be invoked. Should improvement not take place than the tenancy needs to be terminated. This process needs to be part of rules of the site and the tenancy agreement needs to include agreement to the rules of the site.
Plotpod's queries are:
Who is the Landlord?
Can the committee use the 12 month notice rule under the allotments act to terminate a tenancy?
Hopefully to move things on. who signs the tenancy agreement other than the plot holder as this should be the landlord?
Also, have you been able to talk to the Council as to their views as to who is landlord?