The setting is a colony world, with intense volcanic activity and enormous lava pressures outside... magma flooding the underground city is a real threat, with magma-proof-doors between different sections of the city.
The plot: the book opens with the central character in some kind of coffin-sized burrowing machine, making its way through kilometres of solid rock in search of something. This job is some kind of punishment.
Later they find an old spaceship entombed in the solidified lava, and a hand-held particle weapon.
The colony world may be named "Fury"? And there is another much nicer colony world later in the book, perhaps named "Haven"?
There is a central library on Fury, which is being edited by the bad guys to obscure the true history of the colony.
Towards the end of the book we find out that a televangelist controls the lovely green world of Haven, is arranging the deletions from the Library, and arranged for his colony ship to land on Haven while all the other ships were sent to Fury. He also arranged a virus which presumably killed all humans on Earth, shortly after the colony ships departed.
The author is male, possibly English, as I remember reading another of his books which was set in England.