Tomlinson's Relationship With MI6

Tomlinson was dismissed from MI6 in 1995 and briefly jailed in 1997 after attempting to get a book about his experiences working for MI6 published. If Tomlinson had already experienced the punishment for sharing MI6 secrets, what did he have to lose? Why not expose what he believed to be the truth? This almost makes him more believable. But he also had a negative relationship with MI6 and a clear desire for a book deal. It appears neither of them are trustworthy.