Bay trees sprout pretty easily, so there shouldn't be any problem. If you want to play it safe, don't cut back more than a third of the branches at a time. Or you can use the "rule of thumb": don't stub off anything thicker than your thumb. That kind of legginess is usually caused by lack of light, or lack of nitrogen fertilizer, so you might want to check those factors, too.

hi thank you for your advice :o) you might be right about lack of sun light as the trees are in the shade .