  We present spectra obtained with the 10.4 m Gran Telescopio Canarias
telescope of 13 Galactic HII regions, most of them of very low ionisation
degree. The objects are located along the Galactic disc, with R_G from 5.7 to
16.1 kpc. We determine T_e([NII]) for all of them. We obtain - for the first
time - a radial abundance gradient of N that is independent on the ionisation
correction factor. The radial distribution of the N/O ratio is almost flat,
indicating that the bulk of N is not formed by standard secondary processes. We
have made a reassessment of the radial O abundance gradient combining our
results with previous similar ones by Esteban et al. (2017); producing a
homogeneous dataset of 35 HII regions with direct determinations of the
electron temperature. We report the possible presence of a flattening or drop
of the O abundance in the inner part of the Galactic disc. This result confirms
previous findings from metallicity distributions based on Cepheids and red
giants. Finally, we find that the scatter of the N and O abundances of HII
regions with respect to the gradient fittings is not substantially larger than
the observational uncertainties, indicating that both chemical elements seem to
be well mixed in the interstellar gas at a given distance along the Galactic
disc
