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 <answer>Manchester United</answer> 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 <answer>Manchester United</answer> as Arsenal's biggest rivals, followed by Tottenham and Chelsea. A 2008 poll listed the Tottenham rivalry as more important.
What club has Arsenal have an increased rivalry since the 1980s?
Manchester United