Best pruned in late Feb or early March - pruning rules are the same as usual, but you never cut beyond the graft at the top of the stem, so remove dead, damaged, thin/weak or diseased stems first, then any stems which are crossing and rubbing each other, then prune back to the healthiest, outward facing bud above a leaf node, making an angled cut away from the bud to allow rain to run off, all done using clean, sharp secateurs. If there are really long growths, you can reduce those by half or more now to prevent windrock over winter.

Much like bush rose pruning--think of it as a bush on a stick--but there is more emphasis on the symmetry and evenness of the top.

Thanks to everyone