The programme of the JET Octant 8 Neutral Injector Box (NIB) upgrade is the first, and to date the largest, modification of the JET machine approved within the current EFDA-JET framework. When completed in autumn 2002, this programme will result in the total injected deuterium neutral beam power of ~28MW, compared to the present maximum level of ~20.5MW. This paper gives an overview of various engineering activities and experimental trials carried out in support of this ongoing upgrade programme.