A novel technique for increasing the spectral efficiency of millimetre-wave fibre-radio systems by employing wavelength interleaving in conjunction with optical single sideband modulation. is proposed and demonstrated. The technique has been demonstrated experimentally by employing a wavelength interleaved optical add-drop multiplexer and transmission of a 155 Mbit/s BPSK signal at 36 GHz over 20 km of fibre.