We present a fibre laser broadly tunable in a wavelength range from 1058 nm to 1640 nm based on a new type of metallic resonant leaky-mode diffraction grating and three fibre-pigtailed semiconductor optical amplifiers. For TM polarization in Littrow configuration, the grating has experimentally measured diffraction efficiency into the -1st reflected order of more than 90 % over a spectral range of 1417 nm to 1700 nm. The laser covered a spectral range of 331 nm within a tuning band of 558 nm without any adjustment of optics and its tuning range was limited by amplification bands of available semiconductor optical amplifiers.