From ArticleWorld

Agitpop (or agit-pop), is the process of using popular music to present ideology and political ideas. The word itself is a combination of the words agitation pop, and the genre has gained popularity throughout the UK.

Examples of agitpop groups are The Clash and Manic Street Preachers. The following quote from the website of the Manic Street Preachers shows clear indication of why the band is considered agitpop:

" Shortly before the album release, the Manics were the subject of a BBC TV documentary. The 'Close Up' presentation was made with the band's consent, and it gave an illuminating insight into their past. The cameras travelled to the former mining town of Blackwood, in south Wales. It traced the fabric of the band, who were old childhood friends (singer/guitarists James Dean Bradfield and drummer Sean Moore are cousins). It measured the music against the backdrop of the mid-'80s miners' strike, the politicisation of the region and the subsequent disenchantment when the strike was broken." ([1])