bay tree pruning

my bay is about ten feet high and six across, multi stemmed, it's been cut several times in the past but I've let it get a bit too tall now. I'd like to reduce the height before I can't see out of the upstairs window. Can't do it when the birds are nesting, it's a bit of a housing estate. What would be the best time? I'd like to make some sort of shape, nothing elaborate, as it is now it could become a ball or a cone. 

I have one which I clip in the spring /summer into a ball shape ,its now about 5ft and that's how I would like it to stay.you have to shape it buy taking out the lower branches and giving it a clip into shape.

Thanks flowering rose. How late do you think I can do this. By the time the birds have finished with it I tend to feel it's too late in the season. But maybe I should just go ahead  whenever it is. My fear was that new growth would start late in the summer and not be mature enough to stand the winter. Doubt if it would kill the whole bush/tree, it's been there 20 years from a cutting and the base must be pretty well protected by years of dropped leaves

I think I would wait until spring now,I only say this as I think the hard frost might effect it but you could if you thought it sheltered enough.

Thanks, it's not very sheltered here.