I believe this shrub is also called Red Robin and I am not sure when to cut it back so that we get the red tips next year
There is no mention of pruning these in any of the RHS Encyclopaedias or indeed in anywhere I have looked. We have never pruned ours and it has never failed to give a good show.
When we have needed to prune to keep the shrub to a reasnable size, I have done it after the new red foliage has turned green which then gives you a chance to see the final size.If you do it during the winter it will almost immediately get bigger as the new growth comes in the spring. You do see it grown as a hedge quite often again this is cut during the summer.
I have a small one grown as a standard so I have to keep it pruned back. I tend to do it as lauriek, after the red foliage has turned green. It will then usually produce more fresh red leaves which I will trim back again in the autumn if it has got too big again. Last year I cut it back quite hard with no problems.
Thanks everyone