He is also branch secretary in Brent, North London, for the ATL, NUT and NASUWT, meaning that the Easter conference season is an exhausting time for him.
The least welcoming union seems to have been the NASUWT, which stymied Mr Roberts' attempts to make it a hat trick by passing a rule banning officials in other unions from sitting on its executive. And now the certification officer has upheld the decision.
The officer was told that the measure was being quietly referred to within the union's executive as the "Get Hank" rule. Nonetheless, the officer judged that it was reasonable because of a potential conflict of interest if one person was on more than one executive.
Chris Keates, NASUWT general secretary, said the outcome recognised that unions were in competition and that there was a risk that confidential information might be shared.
Mr Roberts said: "There's no way I'm going give away secrets. They were just fearful that somebody supporting professional unity might get elected, proving that the majority of teachers wish there was one strong, united union."