So the question is - what cabling should I use to connect this thing to
the fuse box - or perhaps a question before this is should I actually
hard-wire this into the fusebox. It is physically adjacent to the
fusebox and only needs 2 ffet of cabling.

It should be connected to a 13A FCU, which should be connected to the
consumer unit (or a convenient ring mounted socket) using 2.5mm T&E cable,
assuming the run is relatively short and is not buried in insulation. The
unit can be connected to the FCU using either 1.5mm T&E cable (or bigger),
or using a 13A flexible lead. The FCU can be mounted either at the consumer
unit end or close to the 8 way unit and should be labelled.

If the 8 way unit explicitly allows protection at 32A, then you may connect
using probably 6mm cable and no FCU, although you may have to do a specific
calculation to determine the actual cable CSA required.

Christian.