I’m never certain on the definitions of undertaking or overtaking, I’ve always thought these to be manoevres that involve a change of direction or lane. So, overtaking is moving to the outside of another vehicle to move past it, wheras undertaking would be moving to the inside to pass.
Is carrying on in your lane & passing a slow moving vehicle in another lane an overtake or undertake, or merely passing another vehicle?
On the M4 this evening I passed a row of 3 cars that were in lane 2 (middle lane) whilst I was in lane 1 (inside lane), I passed them because the car at the front (lane hog) braked without reason & I decided not to brake, just carry on at my same speed as my lane was clear for a long way ahead, ending up passing those 3 cars. Did I just undertake illegally?