Lavender should be clipped over twice a year - once after the first flush of flowers is more or less over, taking about half an inch of foliage as well, and again round about late September. You can cut it now if you want, but might like to wait till the flowers fade a bit before you do. Don't cut into old wood, and bear in mind that lavenders are usually replaced about every five or six years because, even with regular trimming as described, they inevitably become woody and leggy.

Thanks Bamboo I think that's what as happen it's about 6 years old it is looking leggy will go back out and have another look at it ,the perfume from it is still lovely so maybe I will leave it till the flowers fade some more .

It's the right time to be taking lavender cuttings - there's a Monty Drone video on the gardeners' world website.