Well leave it for now until March unless you want to lose most of the
flowering to come later. When you prune you are aiming for an inverted
cone shape with sufficient light and air able to reach the centre of the
shrub. Therefore I'd remove at least a 1/3 to 1/2 of the current old
stems at equal distances around the outside of the shrub. I'd remove
most (not all) of any stems old and new that arise from the central
crown of the plant. Of the old stems that remain I'd hard prune down to
2-3 buds from their base. The newer taller outer stems say (2 yr growth
or less), I'd prune by half their length to the nearest bud. You should
then have a basic symmetrical shape, and will only need to do very light
pruning in the following years, removing ingrowing side branches and
continuing to remove more old stems until they are completely replaced
by the newer ones.

Just a quick update. There are flowers to be seen *now* - a couple in
full bloom at the very top (I hadn't noticed the buds when they first
appeared) and quite a few more on the way. There were definitely
flowers late last autumn - I don't know if the current crop are a
result of confusion after my untimely pruning or if this is other than
the bodnantense it was thought to be. There's at least one website
talking about the "dawn" viburnum where a second flush of flowers
bloomed july/august.

Is the march pruning still the best in the light of this do you think?