Hi There,
If your question is- Can user in service BU share records with the users of UK BU?
The answer is yes- just click on the share button after selecting the record and share it with the respective BU user and assign required privilege.
If your question is- Can the user in service BU share records with the users of UK BU which in turn automatically gets shared with the parent/child BUs of UK
The answer is No- its not possible in standard CRM, you can share records only with another user or team. probably what you can do is- whatever entity you want to share, on the security role of service BU user give him organization level privilege to share record and also create teams for a group of users from some department/region
for e.g : Service Engineer wants to share an appointment with the Sales Team of UK & Manufacturing Team of EU
and lets say the service engineer has the security role 'serviceman'
You should provide organization level share privilege to the activities entity (it includes appointments,task and all other crm activities)
The service engineer then can easily share the appointment with UK Sales team & EU Manufacturing Team
If you are looking for automatic sharing on workflow events like change in field, record creation, record assignment etc. you can try this solution- crm2011workflowutils.codeplex.com