Band will join friend Swift for a select number of US dates later this year
Band tweeted photo of producer with caption 'Uh Ohz'
They performed 'Don't Save Me' in the BBC Radio 1 Live Lounge
Jamie T, London Grammar and Twin Atlantic also feature highly
The track is part of Bastille's forthcoming collaborative EP 'VS (Other People's Heartache Pt III)
Alana Haim uploads image showing Danielle Haim playing guitar
The four women joined forces for a feature in the New York Times
A$AP Ferg also appears in 'Dallas Murphy' US chat show spoof
LA trio will begin working on new album soon
Trio have been writing on the road