An executive committee member of the National Graphical Association, Jerrom was associated with the Communist Party’s Print Advisory Committee for many years.
In the early 1980s, he was a national officer of the NGA. In 1983, as the broad left candidate, Jerrom was beaten by Tony Dubbins (NGA assistant general secretary since 1976), in the ballot for NGA general secretary. Dubbins polled 36,921 votes to Jerrom's 19,023.
NGA merged with the Society of Graphical and Allied Trades in 1990 to form the Graphical, Paper and Media Union. (This in turn merged with Amicus, which merged with the T&G to form Unite.)