Chas,
a long time ago I tried to tell my clarinet teacher that I play better ( in time ) when I tap my foot. He responded:
"What controls your foot?" If the passage is too difficult for your fingers, your brain will slow down your hands AND your feet! Tapping does not help keep time. If you "feel" the music - great! Tapp all you want, but don' kid yourself into thinking that you have a sparate metronome just for extremities !