P wrote:

And he's correct. He's wrong to force you to brake, of course - that's bad
observation / bad driving by him - but if he was given a clear lane (yes, I
know he didn't get one, because you were in it), then he doesn't need to
indicate. The rule of the road is to keep left. If a driver is in an
overtaking lane, he should move back to the left hand land when safe.

(When I took my advanced driving test, I was told off by the police class 1
driver in the passenger seat for indicating when moving into a left-hand
lane, and the above was his explanation.)

And I would disagree with you and him. If you are changing your course,
then you should signal your intentions. That is the first principle.
Keep left comes secondary to that.

BTW, where is this 'overtaking lane'? If the traffic is stationary in
queues (as it was) then overtaking can be done wherever and lane
changes should be signalled.

There is no harm in signalling left and if that signal will benefit
someone else then one should do so.

...d