As suggested , the vehicle you saw “pull” the lorry would have been VOSA and NOT HATO.
HATO do NOT use “follow me” on their VMS vehicle message panel and NOR is it an option to use. 
That is also NOT the correct and trained way of a “Safety Intervention Stop” on a vehicle for hato.
and NOT to be mistaken with powers of Law enforcement.
Yes they are trained to use a protocol proceedure in the interests of “Safety Intervention” , and this will take place from behind the said vehicle of concern if necessary , this is to safeguard all road users to point as may be necessary . Other than that , the Police will also take charge as necessary and Police WILL persue any Law Enforcement where necessary and hato can liaise with police to inform them.
3) Those powers may only be exercised for one or more of the following purposes–
(a) maintaining or improving the movement of traffic on a relevant road over which the traffic officer has jurisdiction by virtue of section 3;
(b) preventing or reducing the effect of anything causing (or which has the potential to cause) congestion or other disruption to the movement of traffic on such a road;
(c) avoiding danger to persons or other traffic using such a road (or preventing risks of any such danger arising);
(d) preventing damage to, or to anything on or near, such a road;
or for a purpose incidental to any of those purposes.
It comes under a Traffic Officers powers of the use of Emergency Traffic Management :-
… Traffic Management Act 2004…
opsi.gov.uk/acts/acts2004/uk … 40018_en_1
Traffic officers Powers :-
opsi.gov.uk/acts/acts2004/uk … 1-pb2-l1g5
More info` here too :-
highways.gov.uk/
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Hope this helps and clears things up 
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