An armed off-duty customs officer arrested while allegedly taking part in illegal road racing has been released on HK$10,000 bail. The 32-year-old customs officer, surnamed Lo, was carrying his department-issued revolver while travelling as a passenger in a speeding car that was stopped while racing along the winding Route Twisk, in Tsuen Wan, in the early hours of Sunday. Arrests were made as part of increased police efforts along motorways in the New Territories to combat illegal road trials by racers preparing for November's Macau Grand Prix. Superintendent Patrick Siu Heung-wing said at this time of the year, souped-up vehicles were frequently found tearing along roads like Route Twisk - which runs over a ridge from Tsuen Wan to Shek Kong - and expressways in the New Territories because it's 'too troublesome' for drivers to take their cars for speed tests to race tracks in Shenzhen. The customs officer, along with the 32-year-old driver of the vehicle, and a 20-year-old driver and 19-year-old passenger of another car, were allegedly travelling at about 160km/h, a senior officer investigating the case said. All four men were released without charge on HK$10,000 bail each and ordered to report back to police on November 14. Police returned the gun to the customs officer who handed it into the Customs and Excise armoury on Sunday before taking three days' leave. A Customs and Excise Department spokeswoman said the officer was a member of the Special Task Force, and depending on the operations they were working on, unit members could carry their weapons while off duty. 'The present case is an isolated incident and the department will study it thoroughly to ensure strict compliance by customs officers with the relevant orders and instructions,' the spokeswoman said. 'Given the safety issues involved relating to the use and carrying of firearms and ammunition by customs officers, the department will treat the matter seriously,' the spokeswoman said. Traffic police have been carrying out a territory-wide operation, called Fossington, to combat racing cars which are often fitted with modified engines. Mr Siu said: 'Before they join the grand prix, the drivers will test their vehicles and modify them, so they do speed tests along these expressways.' Unlike in Shenzhen and Macau, there are no racetracks in Hong Kong, so drivers carry out test runs on local expressways and roads like Route Twisk that test their cornering skills. 'They travel at 100 miles an hour and cross double lines. It's extremely dangerous for vehicles coming from the other direction,' Mr Siu said. Convictions for illegal road racing carry a maximum penalty of HK$100,000 and a one-year jail sentence.