Why do I need to transaction report?
The main purpose of Transaction Reporting, as outlined in the FSA’s Transaction Reporting User Pack (TRUP) is to enable the FSA to detect and investigate suspected market abuse (insider trading and market manipulation). Regulators use the data to view all transactions executed. When they receive an allegation of market abuse or identify an issue, the transactions are investigated as a "key piece of the jigsaw in enabling us [the FSA] to determine whether there is a case of market abuse that warrants enforcement action". Similarly, transaction reports are used as evidence when bringing market abuse cases by providing an audit trail of the complete transaction.
With a large database of transaction reports, the FSA also uses the data to aid market surveillance, for example, as an alert to any significant market developments that could affect the stability of the markets. This is facilitated by the passing through of transactions to the relevant authorities, for example, where the primary listing of the security is under the responsibility of a regulatory authority in a different European country.