Getting the truck to a crowd of people large and restricted enough to ensure they don't just simply move out of the way when they see you coming is the harder part.
Getting a HGV illegally is still pretty hard.
As a truck driver, getting hold of an HGV wouldn't be hard and assuming the driver has any degree of experience he'd have little trouble accessing a pedestrian area if he was inclined to do so, the type of truck used in this attack is a 17tonner, such a vehicle would knock bollards etc out of the way like they weren't there, believe me, same for any cars blocking the way.
The kinetic energy in these things is surprising to the uninitiated, let's put it this way, two things will stop an HGV dead, large tress and bridge supports, anything else gets knocked out of the way or smashed through.
