As long as the socket is the same as a British one, you should have no problems. (Various sockets are found in Hong Kong, including the '3 pin round' ones but, as you say, you're most likely to find '3 pin square' sockets).
Hong Kong uses a 220V electrical system (at 50 Hz). The UK uses a 230V system (also at 50Hz) with common plug-wiring conventions. The slight difference in nominal voltages is well within the tolerance limits of most electrical equipment so you shouldn't experience any problems.
Chris