Unfortunately, since it's an "aftermarket" video, the band who performs the song doesn't seem to be credited.
For all I know, this may be the only song in existence to contain the word "Semtex". The entire lyrics can be found here, along with a note that it has been performed by Éire Óg as well as The Spirit of Freedom (I'm not sure which of these groups performs the version used in this video, however). The songwriter is unknown. Other videos exist, set to the same recording, but this is a particularly striking one.
Of course, the song is now out of date, since the decommission that the singers are telling the UK to "stick" did in fact come to pass, thanks to the Good Friday agreement. That is one of the very few things for which Tony Blair may legitimately deserve credit; too bad he went and blotted his copybook with stuff like Yugoslavia, Afghanistan, and Iraq.
And, needless to say, my posting of this video should not be seen as an endorsement of IRA methods, any more than this entry is an endorsement of Janet Greene's politics.