As indicators are supposed to indicate your intention, do you really think the overtakee wasn’t expecting you to return to the left lane? “Oh here comes a McLaren overtaking me - I guess they’ll continue the rest of their journey on the wrong side of the road now”

The sole caveat is of course where you may be picking off a few cars at a time in a row of traffic, in which case indicating your intent to occupy the gap someone else was already maintaining to the vehicle in front is acceptable. “Hi - I intend to cut you up”.
The second sole caveat is where you are on teh motorway and you are on cruise control, sailing past a slower moving vehicle who then speeds up - leaving you “stuck”’out in an overtaking lane. In which case “Hi - I am moving back to the left now whilst muttering that your are clearly incapable of maintaining a constant fucking speed (yc)”.