DAILY checks on Mass Transit Railway carriage couplings will be carried out until the cause of an accident that left passengers stranded in a tunnel is discovered, engineers said yesterday. The Governor, Mr Chris Patten, has appointed a top British rail expert to investigate the accident; while the MTR will complete its own inquiries and present its findings in two weeks. MTR operations director Mr Bill Donald said the ''split train'' had run three services between Tsuen Wan and Central on Tuesday morning before one of the couplings became detached from the front portion of the train at 8.42 am, leaving the rear three carriages behind. Passengers in those cars had to walk back through a tunnel between Tai Wo Hau and Tsuen Wan to reach the station. Services on the line were suspended for almost an hour, leaving thousands of commuters stranded. A visual inspection of the faulty coupling immediately after the accident and a series of tests conducted yesterday at the Tsuen Wan depot did not reveal any problems with the linkage. MTR chairman Mr Hamish Matthews said that, following Tuesday's incident, management had ordered that train couplings be inspected daily before operation. In the past, the couplings were visually checked every 10 days, tested mechanically every six months, and thoroughly dissembled and inspected for damage and possible replacement every 10 years, Mr Matthews said. One of the two ''faulty'' linkages involved in Tuesday's incident was due for a thorough inspection this October, while the other had been checked two years ago. The MTR trains consist of three sections, with three carriages at the front and rear, and two in the middle. The different sections are often separated for maintenance work. The deputy chief inspecting officer of railways in Britain, Mr Alan Cooksey, will lead the government investigation, the Secretary for Transport, Mr Michael Leung Man-kin, said yesterday. Mr Leung said Mr Cooksey, who was responsible for monitoring the Channel tunnel railway, would provide invaluable expertise in an impartial and scientific investigation. Mr Cooksey would examine the results of the MTR's inquiry and compile his own report on the cause of the accident, including any recommendations for remedial work and additional safety steps. This report would be ready for the Governor within two weeks of starting work, according to Mr Leung. ''A five-member MTR panel, comprising company engineers and representatives from both the British train makers and German coupling manufacturers, will look into all possible causes of the accident,'' said Mr Leung. Legislative Councillor Mr Martin Lee Chu-ming led a band of fellow United Democrats to an inspection of the functioning and maintenance of train couplers at the MTR's Kowloon Bay depot yesterday. Mr Lee questioned whether it could be a design fault and Mr Donald said this aspect would be looked at during the inquiry. Legco colleague Mr Albert Chan Wai-yip urged the MTR to permit an independent expert to take part in the inquiry in order to ensure impartiality. Mr Donald said this would be considered.