Without seeing the level of violence and disorder prior to this clip there is no way of judging.
That said one of the perpetrators has smacked a female officer is the face so hard she sustained a broken nose.
In the clip the perpetrators were very clearly resisting. It's an airport, a sensitive area that needs to be tightly controlled. How were the police to know whether this was a distraction from a terrorist incident. They don't. They needed to being the situation under control ASAP.
Now the middle class world of mumsnet may not like it, but these police will deal with scum, day in day out throughout their careers. Thieves, rapists, child abusers, murders, wife beaters. And they will know, sometimes the only way to bring a situation under control quickly is to kick someone in the head to keep them down on the floor.
If that offends you, don't join the police. But don't try and stir up hatred of the police using a tiny clip of what was clearly a much longer incident.