A method of operation of a basestation in a cellular communications network, the method comprising: when the basestation is powered on, and at first predetermined time intervals, entering a first measurement mode, in which the basestation is configured in such a way that it is unable to detect transmissions from attached User Equipment, UE, and can receive signals transmitted from other basestations on system downlink frequencies for first periods, wherein, in the first measurement mode, the basestation can make neighbour cell Radio Frequency, RF, measurements and decode the System Information Blocks, SIBs, from the Broadcast Channel, BCH, of surrounding neighbours; at second predetermined time intervals, entering a second measurement mode, in which the basestation is configured in such a way that it is unable to detect transmissions from attached User Equipment, UE, and can receive signals transmitted from other basestations on system downlink frequencies, and making measurements on the system downlink frequencies for second periods, wherein the second predetermined time intervals are such that the second measurement mode is activated more frequently that the first measurement mode and the second periods are of shorter duration than the first periods so that, in the second mode, only RF measurements can be calculated; and once the measurements in the second measurement mode have been made: transitioning to a normal mode wherein the basestation can receive signals on system uplink frequencies; determining that a significant change has occurred in the radio environment of the basestation, wherein the significant change is a significant change in the RF interference from neighbouring cells; and entering the first measurement mode. when the basestation is powered on, and at first predetermined time intervals, entering a first measurement mode, in which the basestation is configured in such a way that it is unable to detect transmissions from attached User Equipment, UE, and can receive signals transmitted from other basestations on system downlink frequencies for first periods, wherein, in the first measurement mode, the basestation can make neighbour cell Radio Frequency, RF, measurements and decode the System Information Blocks, SIBs, from the Broadcast Channel, BCH, of surrounding neighbours; at second predetermined time intervals, entering a second measurement mode, in which the basestation is configured in such a way that it is unable to detect transmissions from attached User Equipment, UE, and can receive signals transmitted from other basestations on system downlink frequencies, and making measurements on the system downlink frequencies for second periods, wherein the second predetermined time intervals are such that the second measurement mode is activated more frequently that the first measurement mode and the second periods are of shorter duration than the first periods so that, in the second mode, only RF measurements can be calculated; and once the measurements in the second measurement mode have been made: transitioning to a normal mode wherein the basestation can receive signals on system uplink frequencies; determining that a significant change has occurred in the radio environment of the basestation, wherein the significant change is a significant change in the RF interference from neighbouring cells; and entering the first measurement mode. transitioning to a normal mode wherein the basestation can receive signals on system uplink frequencies; determining that a significant change has occurred in the radio environment of the basestation, wherein the significant change is a significant change in the RF interference from neighbouring cells; and entering the first measurement mode.