It's not technically possible to set up a dynamic cross-District shared sub-team on scouts.org.uk. However, there are a couple of options by which to group people together across different Districts. For example, a Campsite Sub-Team or an Awards and Rewards Sub-Team.
In each scenario below, Patch A, Patch B and Patch C want to share team members - as none of them have enough volunteers to set up a full sub-team of their own.
1) When team members don't need visibility access to those below in the hierarchy The sub-team is set up in Patch A and populated with members from Patches A, B and C. This means that those from Patches B and C will also become members in Patch A. In this solution, while the sub-team sits in one patch, its team members are pulled from different patches. [Any visibility will be limited to Patch A.]
2) When team members need indirect visibility access to those below in the hierarchy The sub-team is set up three times; once in each patch (A, B and C). Each team member joins the sub-team in their own patch. However, the Team Leader will join all three sub-teams. In this solution, the team members remain in their own patch, while the team leader links them together by being part of each sub-team. The team leader will have the visibility access of all three patches and can share visibility data with other team members as needed.
3) When team members need direct visibility access to those below in the hierarchy The sub-team is set up three times; once in each patch A, B and C. Each team member (and the team leader) joins each of the three sub-teams. In this solution, all team members (and the team leader) have visibility access of all three patches.