Barely two years old, London City Ballet is flying high – very high, in fact.  The modern-day revival of the original touring company (1978-97), this 15-strong troupe, dreamt up and assembled by dancer, choreographer and entrepreneur Christopher Marney, is creating new levels of excitement in the British ballet world. No wonder Sadler’s Wells was abuzz with expectation as London City Ballet’s current mixed bill, Momentum, reached London as part of an extensive international tour.