This is a simple structure consisting of democratically elected committee members who come together to run the organisation on the members behalf.
The main advantages of this structure are that it is cheap and easy to run. It is also not regulated therefore you are not answerable to a regulator.
Disadvatages of this structure is that it is not a legal entity and therefore the members and the organisation are not seperate. This means that there is very little protection for Trustees.
This structure would be best suited to small organisations carrying out simple, low risk activities who do not own property, employ staff or enter into contracts (such as lease agreements).