Posted: Yesterday at 12:31
you can cut it back now bimsii. Better to wait another week or so for flowers to go over. Not great to cut lavendar in autumn. Cutting it back as soon as flowering is over, in summer, helps the wood to ripen and produce hardier foliage for the winter.
You are right to prune as you do, viz., almost to old wood but still in the green, but it is the timing of it I would address