For both the UK cinema and DVD/Blu-ray release of Robot Dreams, the scene you mentioned was not cut, but did have to be censored.
According to BBFC guidelines, the use of this 'rude gesture' meant that the film could not qualify for a PG rating. One of the great strengths of the film is that it can be enjoyed by audience members of all ages, so we felt that it was important to secure the PG rating so that parents could feel comfortable bringing small children to see it in cinemas or bringing the film home on DVD or Blu-ray.
We worked with the director, Pablo Berger, on this issue and while no footage has been removed from the scene, the middle finger gestures from Robot and the punks were obscured. This was the solution we all felt impacted the film the least, while still complying with BBFC guidelines.