Authorities in Hong Kong and on the mainland have stepped up intelligence exchanges and control of the one-way permit system to clamp down on forgeries. Deputy Director of Immigration Ambrose Lee Siu-kwong said yesterday the department had increased co-operation with its mainland counterpart, which had also tightened controls. Mr Lee said Public Security Bureau officers at the Lowu border control points would be told about every one-way permit issued. 'If officers fail to match the data of the permit holder with their records this may prove the document has problems,' he said. Principal Immigration Officer Leung Ping-kwan said: 'It is impossible for forged document holders to cross the border unless they have got hold of the data of the real permit holders.' Guangdong Public Security Bureau revealed last week it had smashed a syndicate forging one-way permits. Six people were arrested, including at least one Hong Kong resident. Mr Leung said the department had discovered more than 100 forged one-way permits since 1993. Thirty-six of the holders had been repatriated. Those remaining were still being hunted but Mr Leung believed they had already returned to mainland to avoid arrest. The director general of the Ministry of Public Security's Bureau of Exit and Entry Control, Xu Ganglu, plans to visit the territory this month.