The structural and magnetic properties of (Fe 1 - x Mn x ) 3 P compounds, in the concentration range 0.67=<x=<1, have been investigated by means of X-ray and neutron diffraction experiments, magnetisation measurements, Mossbauer spectroscopy and first principles electronic structure calculations. The magnetic ordering temperatures obtained from the different techniques were consistent with each other but different from previously published results. The magnetisation curves and neutron diffraction intensities can be explained by an antiferromagnetic ordering with a magnetic unit cell four times larger than the crystallographic unit cell. The magnetic moments are small as judged from neutron diffraction and Mossbauer spectroscopy results. The band calculations on the other hand suggest a competition between Pauli paramagnetism and magnetic solutions with large magnetic moments.