They will only support BABYMETAL for the 4 UK dates, not the rest of the European tour. We have yet to see who will support them during the rest of the tour.
Tickets and venue info. As of the writing of this, Manchester is sold out, VIP 1 (The Chosen One) sold out for London and Cardiff, and VIP 1 (The Chosen One) and GA sold out for Glasgow.
Their bassist, Sean Scott, had posted this on April 4th, 2016:
Not only did I miss the @BABYMETAL_JAPAN London show but also failed to realise the new album dropped 3 days ago. Downside to being away
To get a taste of them, this is the song with the most views on their YouTube channel:
And they just released this song a few hours ago: