The trials are going to be on motorways only with drivers in all 3 vehicles but with the lead driver in control. Personally I can't see it working. There are too many variables and things to go wrong.
A number of questions on legal matters haven't been addressed yet. i.e. these vehicles will be closely tailgating for aerodynamic reasons, yet tailgating for normal vehicles is illegal. Also, who is responsible in the event of either the 2nd or 3rd vehicle in the convoy having an accident ?
In the event of a breakdown or tyre blow-out, they're going to have to find 150+ feet of motorway hardshoulder on which to stop. It'll cause even more chaos than before on a "smart" motorway.