Head of the Apex union who decided to play by the rules during the bitter Grunwick dispute of the late 1970s
Roy Grantham, who has died aged 86, was a principled, pragmatic, old-style trade union leader. From 1971 to 1989, as general secretary of Apex (now part of the GMB), he significantly influenced the trade union movement and the Labour party on major policy decisions affecting the European Union, government pay policies and single union agreements. His achievement was the more impressive in that it came at a time when the political left of the Labour movement were in the ascendancy and opposed these policies.
Grantham's biggest trade union battle was the Grunwick dispute, where he learned that however just your cause, you can still lose. Grunwick, a mail-order film-processing company based in Willesden, north London, was owned by George Ward who dismissed 137 workers, many of them newly arrived Ugandan Asian immigrants, for striking for trade union recognition. Apex took the matter to Acas which ruled in favour of recognition, but Ward refused to accept the decision. It then went to the high court. which ruled in the union's favour. Ward again would not go along with the judgment and took the matter to the court of appeal, which declared the Acas report void.
When the Scarman report commissioned by the Labour government recommended reinstatement of the strikers, Ward rejected it, effectively ending the dispute. It had lasted two years, starting in 1976. This trade union defeat was made the more galling because throughout one of the bitterest and longest disputes of the period Grantham had tried to win by the "rules", only to be let down by a legal system prepared to search diligently for reasons to disown its previous decision.
Grantham was born in Birmingham, went to what is now King Edward VI Aston school and then became a wartime Bevin Boy. After that he worked for the Inland Revenue. But early in his career his future life was shaped by his decision to become an area organiser for the Clerical and Administrative Workers Union. He became the union's Midlands area secretary in 1959 and four years later was made the assistant secretary, which took him to work in London. During his first few years in the capital the union's membership doubled. In 1970 he took over as general secretary of the union, which in 1972 changed its name to the Association of Professional, Executive, Clerical and Computer Staff (Apex). Apex joined GMB in 1989.
Trade union leaders throughout the 1970s made common cause on the big issues such as the industrial relations bill. Grantham's moderate stance on government incomes policy, which he saw as beneficially affecting his members' pay, did not go down well with some powerful leftwing union leaders.
In 1975 Grantham ordered Apex negotiators to accept the government-TUC guidelines on pay policy. It was also the year he lost his seat on the TUC general council. Throughout the 70s the Labour movement's shift to the left intensified and its effect on party policy became more electorally damaging. Grantham warned successive Labour party conferences, to no avail.
The destructive drift to the left finally hit the wall in the "winter of discontent" in 1978-79, but it galvanised the moderate forces in both the Labour party and the trade unions to organise to regain control. In 1981 Grantham and others formed Trade Unions for a Labour Victory, from which a formidable political force emerged. After a long and arduous struggle, the Labour party's electoral credibility was rebuilt.
The catastrophic job losses and consequent membership drop during the early 80s made trade union mergers inevitable, and although being courted by the Engineering Union, Grantham and Apex chose the GMB, where, as general secretary of one of its sections, he stayed until his retirement in 1991. Appointed a CBE in 1990, he maintained his involvement in politics as a councillor in Croydon until 2002.
Fittingly, as a lifelong teetotaller and practising Anglican, he was for a time chairman of the UK Temperance Alliance.
In 1964 Grantham married Maura Walsh. She and their two daughters, Sarah and Claire, survive him.
• Roy Aubrey Grantham, trade union leader, born 12 December 1926; died 25 October 2013