www.xtec.es/~dpermany/creditvirt/students/ unit4/task1/windonbri.htm

Young British Style - out to shock
British culture places less emphasis on appearance than some other European sultures, where to dress badly is social death. Yet at its youth-focused cutting edge, British style is radical beyond that of any other nation.
British women were the first to bare their knees when Mary Quant produced the mini-skirt in the Sixties. Since then, British youth style has often been anti-fashion; punk style, for example, was never about looking pretty. As punk hit the street in the mid-Seventies, British teenagers stuck safety pins through their noses and wore black ripped bin liners. With their hair coloured bright green or orange and fixed into hard spikes with glue, the first punks shocked the adult world. Later, the Goths arrived, also shocking with their white, powdered faces, dyed black hair, black clothes and penchant for hanging around in graveyards. Bright colours came back with the Acid House movement; followers wore T-shirts with big smiley faces and danced till they dropped at huge Acid House parties - some times under the influence of drugs. Nineties New Agers adopted long hippie skirts and loose clothes, and the Grunge movement from Seattle, USA added its eclectic mix of colours and styles. British street style has had a downbeat glamour that speaks of neither elegance nor wealth, but has an energy and an identity of its own.

I don't know if this is where you got the sentence from but this paragraph explains everything you need to know about British fashion leading the way when it comes to 'youth culture'.

radical - extreme, or (slang) excellent, cool

cutting edge - be at the forefront, lead the way

Leading the way with it's youth oriented fashion, British style is extreme, ultra-cool.

Always the leaders in what's hot in 'youth wear', British style is 'out there'.