Empire of the Saviours by A J Dalton

Empire of the Saviours by A J Dalton (Gollancz £14.99) is the first volume in the Chronicles of a Cosmic Warlord:

“The People are forced to live in fortified towns. Their walls are guarded by an army of Heroes, whose task is to keep marauding pagans out as much as it is to keep the People inside. Several times a year, living Saints visit the towns to exact the Saviours' tithe from all those coming of age – a tithe often paid in blood. 

When a young boy, Jillan, unleashes pagan magicks in an accident, his whole town turns against him. He goes on the run, but what hope can there be when the Saviours and the entire Empire decide he must be caught? There are very few Jillan can trust, except for a ragtag group of outcasts.”