The first demonstration is reported of highly reflecting fibre Bragg gratings written holographically by a single 20 ns excimer laser pulse; reflection efficiencies of 65% combined with 1 nm bandwidths at 1550 nm have been obtained. Single-pulse gratings with FWHM bandwidths of 0.05 nm (6 GHz) have also been produced, to the authors' knowledge the narrowest reported to date.