Not sure what you mean when you say remove growth from the bottom - I'd cut that main stem by half from the top down to force more growth from the base, but its a risk - its just a little bit late, should have been done before 22nd June, or the longest day, and that timing's more important in your part of the world than it is here in the south...

Thanks Bamboo. What I meant was remove the side shoots from the base, but I suppose I'd be left with a standard if I did that. The growth at the top has the catkins forming so I'll leave the main stem until next spring and then cut it down .

Well unless you want a standard, don't remove the side shoots at the base - you want more of those, not less! If those sideshoots grow on quickly you may not need to cut that shoot down anyway, more growth from the base will cover up that bare stem, so see how it goes by next spring.