Just wanted to share this, maybe will be of use to someone?
I have just been to see family in London and we took my DB (9, and dx autism/PDA) to the Laburnum Boat Club for a kayaking session.
They are fabulous, heavily subsidised (£1 for the lesson or a narrow boat trip), and very inclusive with lots of adaptations for different SN. They also run a youth club in school holidays.