The former West Ham and England defender quit within minutes of a setback which leaves the Shrimpers fighting for Football League survival only six points off the bottom of the Third Division table.
News of Martin's departure was broken by the chairman, John Main, when he addressed supporters in front of the main office an hour after the game. "Following this latest result and discussions with Alvin he decided to resign," said Main. Naturally I feel sad that things have not worked out for him but it has not been entirely his fault. Lack of funds has not helped his cause but he is a man of great sincerity and has always put the interests of this club first."
Martin took over as manager in July 1997. Last year they were relegated to Division Three and have since struggled to make an impact in the bottom section. Their Assistant manager, Mick Gooding, will assume control of team affairs in a caretaker capacity.
Hull's winning goal was scored by David D'Auria nine minutes from time.