The Kennel Club website has a list of accredited trainers that may be able to help.
You may find its a phase he's going through - having found some confidence he doesn't 'need' you anymore
. I heard a great saying recently "12 months on the lead equals 12 years off lead" there's a lot of truth in that - at 9 months old he has little impulse control and his hearing is still developing.
A trainer is a great idea but until you find one I would suggest a long line and back to basics - reinforce a stop at distance plus heel work