It can be. Copyright law in UK allows for criminal prosecution where there is deliberate intent or passing-off in a commercial context. However the difficulty of proving intent and the higher standard of proof ('beyond reasonable doubt') required for a criminal prosecution means that copyright infringement is almost always dealt with as a civil procedure with the aim of recovering damages.

Damages in a civil case are tied to the provable losses of the plaintiff plus the costs of the legal action. Civil courts do not act to punish, simply to restore a wrong situation. In theory damages can be increased to take account of flagrancy of abuse but generally the courts will award pretty much the fee that should have been paid for legitimate use.

There is no concept of punitive damages in UK copyright law, unlike the USA where damages can be very substantial for registered works. UK law is clearly only a weak deterrent to infringers as the worst that can happen is that they pay little more than if they had licensed legitimately. Since much of the time their infringements will go undetected, on balance it is sound business sense to be lax about obtaining permission.

This goes some way to explain why infringement is systemic among UK publishers. Although they will invariably explain instances as isolated mistakes, there is little motivation for them to take reasonable care and substantial benefit if they can get away with it much of the time. The practice is so widespread that this can only be a matter of deliberate policy, and the intentional nature means that criminal offences are being routinely committed by publishers, confident that they will invariably escape prosecution. It's a disgraceful way to run an industry.

Criminal copyright prosecution allows for imprisonment and fines, and infringing goods may be seized. It is important to understand that even if a criminal prosecution succeeds, a separate civil case will be necessary to recover financial losses caused by the infringement.