We take them off the bottom of ours to stop them becoming bushy. Don't cut them though, tear them off to pull out the 'root' of the twig. I slide the edge of my foot down the trunk and push them off with that. How much - well the lower branches should be obvious and the rest is just to keep the trunk tidy and to your satisfaction.

If you can catch them young enough, you can just rub them off with a gloved hand. If they are too old and tough to do as Mr. B does, cut them as close to the trunk as possible, to get rid of the buds at the base of the twig--it makes for fewer to do next time.

Thanks, just going out to do it now.