If a customer needing a replacement SIM, as in lost/stolen/broken etc, already has a spare SIM then giffgaff could provision that unused SIM to replace the missing lost broken one.
That way the customer does not have to wait 10 days for a replacement to arrive through the post.
Other providers do this over the phone. The customer needs only to give the agent the SIM number and code and giffgaff will know if the customer was sent that SIM. The agent can request the Tech Team to update the database. All this could be done within hours of the request being submitted to the agent.
When that status of the SIM changes from unused to replacement then the pay back on a SIM used for replacement is cancelled.
This would improve the service to customers.
EDIT = Also would be a great way to distribute NANO SIMs as it would minimise down time for existing iPhone users.