Arsenal's longest-running and deepest rivalry is with their nearest major neighbours, Tottenham Hotspur; matches between the two are referred to as North London derbies. Other rivalries within London include those with Chelsea, Fulham and West Ham United. In addition, Arsenal and Manchester United developed a strong on-pitch rivalry in the late 1980s, which intensified in recent years when both clubs were competing for the Premier League title – so much so that a 2003 online poll by the Football Fans Census listed Manchester United as Arsenal's biggest rivals, followed by Tottenham and Chelsea. A 2008 poll listed the Tottenham rivalry as more important.
Who is Chelsea's biggest rivalry with?