Suspicious Activity Reports

A Suspicious Activity Report (SAR) is a formal report made when someone in a regulated business knows or suspects, or has reasonable grounds to know or suspect, that a transaction or activity may involve money laundering. In the UK, SARs are submitted to the National Crime Agency (NCA).

You don't need proof. Reasonable suspicion is enough to trigger the obligation to report, and it's not your job to investigate or conclude that a crime has definitely occurred, that's what the report is for.

Tipping off

It's a criminal offence to "tip off" a customer, directly or indirectly, that a SAR has been made or that they're under investigation, because doing so could let them destroy evidence or move assets before action can be taken. This is why suspicious activity is reported internally and escalated through the proper channel, not raised directly with the customer.