Yes Vic, the examples you have carefully selected do indeed demonstrate that extreme violence is not the exclusive preserve of black people, nor can they be accused of specifically importing it to the UK.
However, to examine matters that are a little more recent, it seems (certainly in London and some other large cities) that the vast majority (though not all) of knife crime is perpetrated by black people and their victims are usually black. This does set you thinking when black people are still considerably in the minority in the country in general (though not, of course, in many of the inner city areas concerned).
The similarity of recent events with those of forty-odd years ago is that the victims and their assailants come from the same background. In the case of Mods and Rockers, they all knew the likely outcome when they set off on their adventures. The same might be said of the blacks as they roam around the areas where these unfortunate incidents take place.
From my (admittedly rather limited) knowledge of the Caribbean it seems that knife �culture� is more endemic among the male population there and this seems to have rubbed off onto their less well off cousins here, even though many of them are third or even fourth generation UK residents.