If you head over to skrillexlondon.com (which was displayed on the leaflet) you'll see the sign-up page which has a similar image in the background and font to the South West Four website. Also to note that South West Four have had London festival exclusives before, e.g. Pendulum in 2011.
Skrillex joins Chase & Status on the bill, meaning a rather bass-heavy festival. Weekend and Saturday tickets are available now from Ticketmaster.