When driving a vehicle that's being overtaken, are you permitted to slightly increase your speed during or right after the overtaking manoeuvre?

In the photo you are driving on a road outside a town, and a grey off-road vehicle is overtaking you on the left - you are the driver of the vehicle being overtaken. During the overtaking or immediately after it you are not allowed to increase your speed, not even slightly. The answer is: no.

The Road Traffic Act states that the driver of a vehicle being overtaken is prohibited from increasing speed during overtaking and immediately after it. The rule does not say "significant" increase - any increase is prohibited. The reason is obvious: the overtaking driver has judged that he will have time to return to his lane, counting on your current speed; if you speed up, the manoeuvre will take longer, and he may not have time to move back in before a vehicle coming from the opposite direction, or he will have to brake hard. It is similar with "immediately after" - when he returns to the lane in front of you, your acceleration shortens the gap and creates a risk of running into the back of his vehicle. So you behave predictably: you keep a steady speed or slow down slightly, keep to the right edge of the lane and do not react emotionally to someone overtaking you. Slow-moving vehicles, agricultural tractors and vehicles without an engine must move as far to the right as possible to make overtaking easier.

Legal basis: Art. 24 para. 6 of the Road Traffic Act (Prawo o ruchu drogowym)