(Mr MC posting)
what order and how close? Close protection officers drive big fast 4x4s (so they can smash johnny terrorist out of the way), and a typical convoy would be 2 4x4s and the principal in a normal, quality motor in between. Ive been passed by a convoy of trainees and the 4x4s will ride very close to the car to prevent johnny terrorist (or Mr Mondeo, they dont know who is who) getting in between them and will bully people out of the way.
I'm in Oxford, but my advanced driving and surveillance courses took me to the south coast, most of wales, the fens, and as far as tebay for lunch for a dedicated motorway day. They go where the good roads are, and also where the national speed limits are, as the +20 rule discussed in another police driving thread is applied in training and usually interpeted to apply to posted limits not the national. So we could only do 70 in a 50, but *cough* considerably more in a 60.