THE moment Chris Patten leaned over a tennis net last week and reminded Sir David Ford who was numero uno around these parts was the cue for the Chief Secretary to prepare to leave town. So at the weekend, Keeping Posted joined a select gathering of the territory's good and great at a private room in the Regent where Sir David and Lady Ford were being accorded a farewell dinner prior to their departure to take up a new posting in Britainnext month. The theme of the occasion was captured by a giant ice carving of a junk, which one of the organisers of the evening, Sally Leung, described to us as ''signifying smooth sailing on the next part of the journey''. Then, spooning out a large helping of the caviar that was placed by the carving for your columnist, Sally commented: ''This is Beluga caviar, nothing but the best for the Fords.'' Sally, who was with her husband Henry, hosted the supper together with David and Christine Wong, Jack and Madelaine Tang, George and Lily Chao, Andrew and Jacqueline Liu and Eleanor Wong. Sir David reported no discernible aches and pains from his tennis encounter with Patten, but did point out that the $1-million prize money that was donated to charity from the (grudge?) match took him a year to put together. Farewells are always occasions for reflection and Lady Ford was doing just that. She told us that having lived in Hong Kong since the age of 17, the move back to Britain next month was going to be a major wrench. ''I've always considered myself as belonging to Hong Kong,'' she said. ''So the real sadness about leaving is feeling that you don't belong here any more. ''But looking at it from another side, the move will give us an opportunity to see more of our children, who live in England.''