I have been using a salon (opposite Goldhawk Road Station) called Snippers for many years, as have several of my friends.
I have found them excellent and very reasonably priced.  Mostly we have used Steve (co-owner with his wife Christine), but last couple of years have been very happy with Cathy too.
The salon perhaps looks a little dated, but the cutting and styling is excellent and Steve is worth a try.  Phone:  020 8743 8704