https://www.slab.org.uk/guidance/continuity-of-representation-outwith-solicitors-period-of-duty/
You may act for a client whose sentence is deferred after a plea of guilty and appears from custody on a separate charge, outwith your time as the duty solicitor.
In these circumstances, the client may benefit from being represented by you (the original solicitor) as you are already familiar with their circumstances. We would be sympathetic to a request that you should act in this situation.