Just something I spotted on the Official FA Rules page...
the occupants of the technical area:
are identified before the start of the match in accordance with the competition rules
must behave in a responsible manner
must remain within its confines except in special circumstances, e.g. a physiotherapist/doctor entering the field of play, with the referee’s permission, to assess an injured player
only one person at a time is authorised to convey tactical instructions from the technical area
Read more at http://www.thefa.com/football-rules-governance/laws/football-11-11/law-1---the-field-of-play#m41aHJt4iYbSYm3R.99
Note the bottom line (underlined).
Something to watch out for in future, when opponents' manager, physio and substitutes all jump up shouting at the linesmen or referee!