https://www.slab.org.uk/faqs/firms-merging/
There are several points to settle Ii your firm intends to merge with another before contacting us to enter the new firm on FAMS. These include:
The merging firms may also have accounts they have already sent us that are currently waiting to be paid. We will pay these into the bank account of the firm shown on the Account Synopsis Form. The firm should ensure that the correct firm and branch code are recorded on the Account Synopsis Form for future accounts.
Each of the parties concerned must confirm in writing any decisions the partners within each of the former firms make that would affect details we hold.
Within three working days of being told in writing of the merger we will:
Merging firms should also consider whether the procedures (for civil or criminal) used by each firm will remain the same or whether they will be consolidated into one common version.