"One Step Beyond"
From TheChels.info - The Chelsea Football Club Wiki
"One Step Beyond" is a tune written by Jamaican ska singer Prince Buster as a B-side for his single "Al Capone". It was made famous by London band Madness who covered it for their debut 1979 album of the same name. In recent years the tune has been played at Stamford Bridge following high profile victories; particularly following second leg wins in the UEFA Champions League knock out stages or particularly significant league matches. 
Ska music has been popular among much of Chelsea's support since the 1960s, when the style was introduced from Jamaica and quickly gained popularity among mods, and later skinheads; London youth subcultures whose adherents made up swathes of Chelsea's match-going fanbase. Another ska tune, "The Liquidator", was first played soon after release in the late 1960s, and is currently played as the teams enter the field at Stamford Bridge.
Madness are a band with a close association with Chelsea, with lead singer Graham "Suggs" McPherson and drummer Dan "Woody" Woodgate both being long-time match-going fans.  Suggs wrote and performed "Blue Day" as the Blues' official song for the 1997 FA Cup Final, and Woody has appeared as a guest on Chelsea TV.
The tune is largely instrumental, but the Madness version features a spoken introduction from Chas Smash:
Hey you, don't watch that
This is the heavy heavy monster sound
The nuttiest sound around
So if you've come in off the street
And you're beginning to feel the heat
Well listen buster
You better start to move your feet
To the rockinest, rock-steady beat
One step beyond!