I recently travelled from Embankment to Tower Hill on a Circle Line
train.

When it was moving, every ten or twenty seconds, the acceleration cut
out with a violent jerk and there was that loud popping noise. I am
not exaggerating; it happened constantly the whole way, and the same
thing was still happening as the train left Tower Hill.

So three questions spring to mind

1) Is this something to do with conditions on that part of the line?

2) I've often been in an LU train where there is occasionally a
similar jerk and popping noise. It may be something to do with having
to ease off for a speed restriction or something, or maybe when the
power is cut due to wheelspin, but I don't understand why it's
possible to simply slow down and stop normally at stations without all
the jerking and popping, but not between stations.

3) Does the driver have any control over this, ie is the power being
cut by some automatic process or could they drive more smoothly if
they wanted to?