A pair of Swiss businessmen who have been prevented from leaving Libya for more than a year are to face trial on tax evasion charges.The men, who are also facing visa irregularity accusations, were detained after the arrest in Geneva last year of Muammar Gaddafi’s son in an incident that caused a diplomatic row. Hannibal Gaddafi was held on charges, later dropped, of mistreating two domestic employees. A Swiss delegation headed by President Hans-Rudolf Merz travelled travelled to Tripoli to apologise and ease strained diplomatic and business ties. But they failed to secure the release of the businessmen who also face claims of flouting rules set out for companies working in Libya. In response to the charges, Switzerland says it has suspended an agreement to normalise relations. When the row erupted last year, Libya cut oil supplies to Switzerland and withdrew more than three billion euros in assets from Swiss banks.