Blackberry Picking 

Refers to a rum bunch of fellows that intend to visit a wealthy part of town to steal expensive mobile phones from peoples' pockets.

Blackberry; a popular brand of mobile (cellular) phone.
Picking; Pick pockets

A bunch of thieves might say "We're going blackberry picking up west" (Up west referring to the West End of London)

Blackberry Picking by stimpetta November 2, 2011