The biker died trying to escape pursuing police

The court heard they drove a car into the front doors of the shop in central London, last October.

But police were lying in wait and as they tried to escape, a fourth member died when he crashed his motorbike.

James Nicholson, 19, Anthony Bates, 18, both of north London, and Nicholas Walters, 21, of no fixed address, had pleaded guilty to attempted burglary.

Walters, who was involved in a high speed police pursuit, also admitted dangerous driving.

'Carefully crafted'

Misha Neering's getaway motorbike spun out of control, smashing into the path of a pursuing patrol car.

Another gang member - not named for legal reasons - who was seriously injured in the crash has since recovered but has not yet faced legal proceedings.

Blackfriars Crown Court heard the men were part of a loose criminal collective behind dozens of similar lucrative heists.

Philip Bennett, prosecuting, said the attempted burglary was "a meticulously planned and carefully crafted attack".

Some �7m worth of jewellery was on the premises - most of it easily accessible in display cabinets.

But it was thwarted by a police operation set up following a series of similar raids in the Sloane Street area.