URBAN taxi drivers leave for their first trip to Beijing today, anxious to know what China's policy towards them will be after 1997. Legislators have criticised the visit as an unnecessary pilgrimage, saying some people treat Beijing's views as ''imperial orders''. But the Taxi Association Federation insists it has good reasons for meeting Chinese officials. The 18-strong delegation will met officials from the Hong Kong and Macau Affairs Office tomorrow, to discuss the taxi licensing system after 1997. ''We hope they can give us a guarantee on the issue. There are a lot of worries among taxi drivers about their future,'' said spokesman Ng Kwok-hung, adding the group would also urge the Chinese authorities to allow taxis to cross the Shenzhen border. United Democrats legislator Cheung Man-kwong said the Beijing trip was unnecessary since such problems and suggestions could be communicated through already-established structures, such as Hong Kong affairs advisers.