A number of witnesses reported that he said that. Yes, Britain First is nationalist group. It's leader, Paul Golding, was the one who turned his back on Sadiq Khan when the London mayoral election result was announced. He's a former member of the BNP and National Front. Britain First has launched an enquiry. No doubt the finding will be that Tommy Mair (the suspect) was not acting under Britain First's instructions, but it has been revealed that the suspect did have links to the Swinton Circle and Springbok Club, both of which are white supremacist groups, which hated any non-white person and Jews and were passionately against the EU (and anything else vaguely foreign). It's possible he was 'radicalised online'. It's easy enough to Google both of them.