A Herald investigation has revealed over 30 Federal MPs have failed to declare free gifts and trips, as well as the donors behind them, for close to two years.

The failure of the MPs to update their register of interests in spite of parliamentary requirements has raised concerns about transparency and potential conflicts of interest, with 7 MPs having added nothing since September 2016.

MPs are required to register gifts valued at more than $750 if received from official sources, or more than $300 if received from others.