Are there any restrictions on the right to bring a private prosecution?

Yes. First, all magistrates have a judicial discretion to refuse to issue a summons or to set aside a summons once issued. The decision to issue a summons (or a refusal to set aside a summons) can be challenged by way of judicial review. Second, the Director of Public Prosecutions (DPP) can take over a private prosecution at any stage and may choose to either continue with or discontinue the prosecution. Third, the ability to prosecute certain offences is restricted either expressly by legislation and/or as a matter of policy.