LONDON, Jan 20 (Reuters) - A British survivor of the Algerian gas plant siege described on Sunday a nerve-racking escape across a stretch of desert and a moment of terror when he feared he had fallen into the hands of the hostage takers. The Algerian authorities say at least 23 hostages and 32 militants were killed in the four-day siege, a preliminary death toll they expect will rise when they have finished clearing out the remote gas plant deep in the Sahara. Hundreds of Algerian workers and scores of foreigners escaped.