GUESS who's back in town? It's British TV's ''all-action girl'' Anneka Rice, who started her now-soaring television career on the small screens of Hongkong. Not that we can claim any credit for her success. Anneka's stint here was notable more for its inaction. From fulfilling tasks such as announcing, Anneka (always Annie to her friends) tried desperately to break into children's television, but to no avail - her fledgling career getting stalled in the petty bickering that is endemic to local television. Anneka, who is staying at the Conrad minus TV producer husband Nick Allott, but with children, Thomas and Joshua, and nanny Judy in tow, was yesterday overheard saying that ''some faces from the past were popping out of the woodwork''. She is here as host of a six-part BBC programme entitled Passport, in which two British couples are taken to a distant land and asked to compete various tasks. Until they get to Heathrow or Gatwick airport to catch their outbound flight, the lucky contestants are not told their destination. The first task given to the couples when they arrived in Hongkong was to get from Kai Tak to The Peak using six different modes of public transport. The perfect remedy for getting rid of any lingering signs of jet-lag. For the winner there is the bonus of an extra all-expenses paid week in Hongkong - and possibly a guided tour from erstwhile resident Anneka.