As a current SVFR controller, I can say that although we rarely clear aircraft to cut the corners, and rarely helicopters ask to do it, occasionally you will see aircraft cut the corners. This happens a lot on H3 between Barnes and Thorpe (Though it is a very difficult route to follow from the air). It happens occasionally on H4, which should be fairly easy to follow though. (We will sometimes ask helicopters to cut the corner between London Bridge and the I.O.D if we have traffic that might effect into/out of London City and the helicopters are in a hurry.