Hello Special Mum
I strongly recommend Dr Josephine Stork a neuro diversity specialist in ADHD and ASDA and a great chartered educational psychologist
Her contact details are : email@example.com
and she has a private practice in South Kensington. She is one of the best in the field and her report writing is first class.
Not sure what SEN needs your teen has, but if you want some hope and optimism, you may enjoy my book 'My Child's Different' which tells the story of my own neuro diverse son, who was by the age of seven excluded from three schools in so many years and with the right support and educational environment, he had a transformational journey from difficult child to entrepreneur
Good luck Special Mum
Elaine @The Parent Practice