I have a Hebe in my garden and it as become a bit leggy and most of the foilage is at the top,I just wondered if I can cut back hard and when is the right time to do this.
Hebes are a bit difficult to catch at the right time. If you cut them back now you won't have any flowers next year. If you wait until they have flowered the temptation is to let them grow.
Ideally, they should just be left to do their thing. If you really have to keep them in check, I'd wait until after they have flowered next year. Then I'd go rather cautiously about your pruning as they might take fright and die back.