If this is a Tree Mallow (Lavatera) it can be reduced in height by about a third now and hard pruned nearly to ground once you see new growth from base in spring.

My advice is to leave it well alone until Spring - a hard winter will cut it down anyway, so see what you've got left come the next growing season, when you can reduce all stems down to 6 inches if you want.

Both good advice - Ojibway's if its windy, Bamboo's if its sheltered.

I find they can be brittle and snap in the wind so I tend to reduce a bit before winter and do the rest in the spring.

Many thanks to all who have replied. My worries are over. pef.