Rule 18 of the High Court Rules, requiring leave to sue the President, is inconsistent with and overridden by section 4 of the State Liabilities Act and section 31K of the Constitution, which permit proceedings to be instituted against the President in his official capacity as of right. Where there has been non-compliance with Rule 18, the court may exercise its discretion under Rule 4C to condone the departure from the rules in the interests of justice, particularly where the applicant has presented a substantial cause of action that is not frivolous or vexatious. The test is whether a reasonable court would have granted leave under Rule 18; if so, the court may condone non-compliance. Rule 18 was intended to prevent harassment by frivolous or vexatious claims, not to deny access to justice to persons with substantial causes of action.