It is often tempting, but the problem with this rears it's head if the wazzock you are blocking from cutting in believes his indicators are like a shield of steel, then the resultant accident might be decided to be 50/50. Even though it is the other guy's fault, they might decide "Andrew could have braked to avoid a collision", or might even decide "Andrew put himself deliberately in the way of the other car"...
Accidents seem to be blamed on the providors of all contributing factors, not just the big mistake that causes the smash. I knew an idiot who got off with a 50/50 for a head-on collision where he was rounding a parked car on the wrong side of the road, on a blind corner, in excess of the speed limit. All because someone saw the other car was also travelling too quickly up to the corner. If she had kept to the speed limit he would have probably been given all the blame.
However, it is amazing how a stranger, who's opinion means naff all to you, can extend his middle finger and get you pretty angry if you are in the wrong mood that day. If a guy in the street did that to you as you walked to the shops, you probably wouldn't even break step let alone confront him. But, travelling at 90mph on a busy motorway, people are prepared to chase and sit 6 feet behind the gesturer whilst shouting at the gesturer's rearview mirror (here's a tip Merc-repman, I can't hear you
). At the least the stress of doing this will ruin what should have been a pleasant drive for them, and at the worst can end up with a big smash with lots of dead people.
I've noticed the Skoda website says "*Where the law permits ", with regards to acceleration.