A method of detecting leakage from a tank containing a product , using a radar level gauge system comprising a transceiver , a propagation device coupled to the transceiver, and processing circuitry coupled to the transceiver, the method comprising the steps of: performing a sequence of monitoring operations, each monitoring operation including the steps of: generating, by the transceiver, an electromagnetic transmit signal (ST) exhibiting a time-varying frequency; propagating, by the propagation device, the transmit signal towards a surface of the product in the tank; returning, by the propagation device, an electromagnetic reflection signal (SR) resulting from reflection of the transmit signal at the surface back towards the transceiver; receiving, by the transceiver, the reflection signal; characterized by forming, by the transceiver, an intermediate frequency signal (SIF) for the present monitoring operation based on the transmit signal and the reflection signal; determining, by the processing circuitry, a phase (F) of the intermediate frequency signal for the present monitoring operation; determining, based on the phase of the intermediate frequency signal for the present monitoring operation and the phase of the intermediate frequency signal associated with at least one previous monitoring operation in the sequence of monitoring operations, a measure indicative of a present rate of change of the phase of the intermediate frequency signals for the sequence of monitoring operations; comparing the measure indicative of the present rate of change of the phase with a predefined threshold value; and determining a presence of leakage based on the comparison; and providing, when it is determined that leakage is present, a signal indicative of detected leakage. generating, by the transceiver, an electromagnetic transmit signal (ST) exhibiting a time-varying frequency; propagating, by the propagation device, the transmit signal towards a surface of the product in the tank; returning, by the propagation device, an electromagnetic reflection signal (SR) resulting from reflection of the transmit signal at the surface back towards the transceiver; receiving, by the transceiver, the reflection signal; characterized by forming, by the transceiver, an intermediate frequency signal (SIF) for the present monitoring operation based on the transmit signal and the reflection signal; determining, by the processing circuitry, a phase (F) of the intermediate frequency signal for the present monitoring operation; determining, based on the phase of the intermediate frequency signal for the present monitoring operation and the phase of the intermediate frequency signal associated with at least one previous monitoring operation in the sequence of monitoring operations, a measure indicative of a present rate of change of the phase of the intermediate frequency signals for the sequence of monitoring operations; comparing the measure indicative of the present rate of change of the phase with a predefined threshold value; and determining a presence of leakage based on the comparison; and providing, when it is determined that leakage is present, a signal indicative of detected leakage. <EOS>