The light at the bottom of the world
(Book)

Series information from Goodreads.com.

Teenaged Leyla McQueen, who lives beneath the ruins of a submerged London in 2099, joins a prestigious submersible race in the hope of clearing her father's name before encountering government corruption and a hidden world.

Great Britain, the last days of the twenty-first century. Sea creatures swim among the ruins of Big Ben and the Tower of London, and citizens waver between fear and hope; fear of what lurks in the abyss, and hope that humanity will soon discover a way to reclaim the Earth. Leyla McQueen is chosen to participate in the London Submersible Marathon, she sees is an opportunity to save her father, who has been arrested on false charges. When the race takes an unexpected turn, Leyla will have to defy a corrupt government, deal with a hotheaded companion, and risk capture-- or worse.