Colour centres in diamond are important for potential applications in quantum information technology. Centres based on Ni have attractive properties but the structures are still not fully understood. One interesting colour centre is NIRIM-2 which emits around 884 nm and is based on Ni preferentially incorporated into the <111> growth sector during high-pressure high-temperature diamond growth in the presence of a Ni catalyst. To help understand the structure of this colour centre a combination of Rutherford backscattering spectrometry (RBS) with ion channelling and particle induced X-ray emission (PIXE) with 2 MeV H and He ions has been used to study the location of the Ni atoms in the diamond lattice. The Ni concentration, typically below 25 ppm, is well below the detection threshold for RBS, but the yield of characteristic Ni Kα X-rays shows a decrease when the ion beam is channelled into the <111> growth sector of the diamond. This suggests a significant fraction of Ni is incorporated substitutionally in the diamond lattice. Correlation of Ni location in the diamond host with optical properties of Ni-related centres in the same growth sector of the diamond offers the possibility of advancing our understanding of the structure of these important optical centres.