Undertaking car causes a collision

Paignton, Devon 11-11-2016. Can I ask if I'm at fault please? Turning left into a tight drive, I used some of the right hand side lane. Started indicating 100yards before and travelling at 15mph when I was undertaken and made contact! The camera vehicle is a transit van carrying a 12 foot trailer making a sharp turn into a driveway with a narrow access. www.hgvdashcamfootage.com