cultural or fashion movements taking place in Britain today that could classify as forming a collective identity....

A movement in fashion has brought about a style in young people that resembles a Public school "preppy" image, with people wearing Jack Wills rugby tops and Abercrombie lumberjack style shirts, Barbour coats and leather boots.  Rather than sharing the same beliefs they share the same attitudes to fashion and clothing which is creating a collective identity.
Fashion movements are able to develop and change quicker than cultural movements. Over the last 20 years Mods and Skin heads have faded out and an Indie culture is developing. There is not so much of a stereotypical image of an Indie "kid" as there was a mod or skin head, because with in the culture, the idea is to be as individual as you can.  With the indie scene, there is an Indie style of music, deriving from rock/pop/electro and putting a unique stamp on it. The range in style is diverse and because of this has its independent name.