Guidance on safely and legally separating shared systems, services and data when local government reorganisation (LGR) requires councils to split rather than merge.

What disaggregation involves

Disaggregation is the process of separating joint services, shared management teams, IT systems, databases, infrastructure, and supplier arrangements into set-ups that support each new council independently.

In practice, you may need to:

  • split datasets
  • separate infrastructure or networks
  • separate teams
  • negotiate new supplier contracts
  • migrate one council’s data into a new platform
  • creating standalone reporting and business intelligence (BI) models
  • confirm there is still a legal basis for sharing data

Local Government Association (LGA) findings show that data disaggregation is a complex task, as it requires legal, technical, operational and cultural alignment. You may also need to negotiate with a vendor to access to your own data, which can be an additional cost.

Disaggregation priorities

  1. Systems and services that contain high-risk personal data, support statutory duties and pose legal or safeguarding risks if mishandled.
  2. Systems reaching contract end or renewal can create pressure to start planning disaggregation early. You should assess whether splitting or replacing the system is more cost-effective and negotiate temporary extensions if needed to maintain continuity. Some system contracts will specify how disaggregation needs to take place.
  3. Finance, payroll and HR systems must work from day one. If a shared system needs to be split, treat this as a top-tier risk, as failures will undermine the new council’s stability.
  4. Failing to maintain datasets needed for reporting and legal compliance could expose your council to sanctions or reputational damage. Make sure you can continue to submit statutory returns to MHCLG, DfE, DHSC and the Home Office, as well as regulatory reports and datasets covering social care, homelessness, housing and education.
  5. You can safely sequence lower-priority areas for disaggregation after day one. These include legacy intranet content, low-volume services, historic archives with no current operational use, non-critical workflows, CRM systems where forms still point to legacy processes and legacy reporting dashboards (if stable).

Data security, sharing and quality

Adult and children’s social care data is crucial for safeguarding. Fragmented services may need information-sharing agreements in place for the new council to continues to have access.

Data and records will most likely be split using postcodes, so make sure postcode data on client records is accurate and complete before migration.

Considerations for planning records 

Do not rely on postcodes alone to split planning records. A planning site can: 

  • cross a postcode or council boundary 
  • be located on land with no postal address 
  • have an address that has changed since the application was determined 

Before splitting records, agree with the other councils involved: 

  • which council will hold each group of records and how the councils will access them 
  • which fields decide the split. Postcode may be one of them but UPRNs, site boundaries and which councils carries out the function may be equally important 
  • how you will handle records that cross a boundary or do not have reliable location data 

Before applying the approach at scale, test it against known awkward cases, including cross-boundary sites and records with missing or poor quality address data. 

Historical records

Historical records may even be on paper due to the long retention period for records such as adoption.

The LGA has created a data sharing principles and checklist, outlining the key points to consider when data is being shared between councils as part of the LGR business case process.

Data gathering and retention

Councils of all sizes look after large quantities of data, and the process of combining it to create new unitary councils is a large task. It becomes even more complex when there are two or more new unitary councils.

Councils can reduce the amount of data that they bring into the new council(s). This is particularly true of unstructured data that often sits in network drives or in cloud storage such as Sharepoint or Google Drive. This data – documents, spreadsheets, presentations, photographs and all sorts of other files – can steadily increase to use many gigabytes of storage. Asking teams across the council to review and delete any unnecessary files can be very helpful.

Councils may also be sitting on archives of data from line-of-business systems. Often when a new system is implemented, a backup of the data from the old system is kept in case of system failure. LGR provides an opportunity to review the risk around deleting that data and simplifying the job of migration.

Finally, all the councils should review their policies around data retention and agree new policies for the new council(s). These policies should then be applied to the data being transferred to the new council(s) as it should help reduce the burden of migration.

Considerations for planning records 

Before you move planning records into an archive, check that: 

  • an officer reviewing a live application can still find and read the planning history for the site 
  • an enforcement or appeal case can still be evidenced, including the original case, its documents, and everything that happened afterwards 
  • a local land charges or property search enquiry can still be answered accurately and within the statutory timescale 
  • the links between cases, documents, sites and later decisions survive the move 

Officers may need access to historic records at any time. An old permission, condition or enforcement notice can be the document needed for a live case, so do not apply a single cut-off date across all planning records. 

You should confirm: 

  • who will provide access to archived planning records 
  • how authorised staff will search and retrieve them 
  • how long records are available 

Agree the approach with your information governance and legal teams. 

“Migrating data is eye-wateringly expensive. I still haven’t worked out why. So plan to archive as much as you can in advance.”

Madeline Hoskin, Assistant Director for Technology, North Yorkshire Council

Watch: Devolution and data – building a secure compliant future for councils

In this webinar, the LGA shares the practical steps councils can take to secure their data estate, meet regulatory obligations, and build resilience for the future. It covers planning, governance, risk mitigation and continuous compliance.

Watch the recording