I'm not casting accusations, I've had a good close look at the photos.
As a Heavy Haulage driver, I'd be interested as to why the driver came off the M4, there's no weight limit on that section of the M4 (some flyovers have 100ton weight limit). At that weight all the TTs have a movement order and your not supposed to deviate off your route except in a emergency.
Back to the crash, looking at the photos, are the cones there for a set of road works shutting the nearside lane? If so, from looking at the photographs, that silver hatch has decided to come up the nearside and bully their way into the front of Truck. It's happened to me loads of time, cars coming up the blind side.
Anyway that's the way it looks...