This book is set in London about a young boy. He has a brother who is a bully. He is reading Ancient Mariner at school and he discovers an old boat to go down the canal on. Unfortunately this is the only information I have. I really hope that you can help me! Thanks.
I vaguely remember reading a book with that plotline about 25 years ago. After much searching, I found the one I read: The Secret of the Missing Boat, by Paul Berna. I don’t know if it’s the one you’re looking for, but it might be worth checking!