Basically yes it is ok to show crowds of people being blown away, it will be now usually just be given an uncut higher UK rating depending on what the level of violence, the rating is then based on the level, but it isnt ok to have a headbutt at a certain low UK rating it will be cut unless the distributor(Lucasfilm? Fox) take the higher rating offered by the BBFC another example is Indiana Jones and the Temple of Doom that is cut over here in the UK because the distributor refused the higher rating and wanted a more audience friendly lower rating ,some distributors do that over here sometimes(very very rarely now thankfully) they are offered a uncut higher rating but go with the lower cut rating, this is why i import a lot of my discs to be certain,