Unincorporated association
You can be constituted as an unincorporated association. All you need to do is draw up and agree a constitution to help your group run smoothly.
Because you don’t need to be a charity or have limited liability, you don’t need to worry about registering with any external organisations such as the Charity Commission or Companies House.
An unincorporated association is a membership organisation, so you should be clear in your constitution what your membership criteria are. Your answers suggest you want strict criteria which limit who can become a member. Some funders prefer to give grants to organisations with open membership structures, so if you are hoping to get grant funding you may want to go back and consider being open to new members.
Your route so far:
Open group? No Workers in control? Yes Reinvest surplus? YesWorkers paid? No Want to be a charity? No Need to be incorporated? No