Hi Bradders
In its simplest form the site association needs no paperwork at all and if you're a friendly bunch and you just want to organise the odd site bar-b-que or discount seed scheme then that's fine.
If the site association wants to do a bit more, particularly if you'll charge a membership fee and if there's the possibility that anyone will question how you conduct your business then it's best that the association has a Constitution to define formally what the association is and how it works. I'll PM you my association's Constitution.
Note that the Constitution governs the operation of the site association, it says nothing about how the allotment site is managed. What goes into the Constitution is more or less up to the association, but there are quite a few available on the web and NSALG have one too.
If the site association is actually going to manage the site then it gets a bit more involved. An unincorporated association is not a body corporate and so it's necessary to create a trust to own any lease and the trustees have to understand their obligations carefully. There are also other legal entities that might work better than an unincorporated association. The
Charity Commission has some advice.
The Rules are the things that the allotment tenants must and must not do, but you have very little scope for changing the existing Rules. You need to understand that the Rules are terms in a tenancy contract between the tenant and landlord, so if you're not the landlord you can't tell the tenant what to do. If you are the landlord you're limited in what changes you can make to the rules for existing tenants by the Unfair Terms in Consumer Contract Regulations, and if the site is a statutory council site you only have the power to make rules under S.28 Samall Holdings and Allotments Act 1908 - so that's mostly the conditions under which the plot is to be cultivated - most councils go nuts and make rules about all kinds of things, but they might have a job to enforce them.
If you're talking with the council about rules you need to be talking about the tenancy agreements too.
I'd recommend you start with
The Law of Allotments by Paul Clayden, and there's a sample set of Rules in there that have been widely used by councils.