What should a broker do if they suspect suspicious activity after a transaction?

When a broker suspects suspicious activity following a transaction, the appropriate action is to submit a Suspicious Transaction and Order Report (STOR) to the Financial Conduct Authority (FCA). This step is crucial because it helps regulatory bodies monitor and investigate potential financial crimes, such as money laundering or fraud. By filing a STOR, the broker is fulfilling their legal and regulatory obligation to report any activity that may indicate illicit behavior. This protects not only the integrity of the financial markets but also upholds the broker's compliance with regulatory standards.

Directly contacting the client may not be advisable as it could alert them and potentially compromise an ongoing investigation. Notifying other brokers is also not appropriate; such matters should be handled through the proper regulatory channels. Ignoring the suspicion could lead to serious legal repercussions for the broker and further facilitate any illegal activity. Therefore, submitting a STOR is the best course of action.