My daphne is getting too big and 'leggy'. Can I prune it back.

I would hesitate to prune back a Daphne that only has leaves on the ends of the branches as there is nothing left for it to produce new leaves on.
I think the problem here is that the shrub is planted in the shade, hence the lack of leaves in the middle of the plant. Here in Moray I grow my Daphnes in sunny positions and have no reason to prune them.
Personaly I would leave it well alone, Sutherland.

They don't mind you removing dead, diseased and damaged wood, but don't take kindly to hard pruning.

I was reading the other day that the way to propagate Daphnes was to mound up earth around them and after a year or two they would send out roots from the individual stems and you could sever and replant them. Just a thought!