Final answer:
Frank Cousins becoming Secretary of Transport Workers in 1956 meant that Hugh Gaitskell could not rely on votes from the trade unions, which had considerable influence within the Labour Party.
Step-by-step explanation:
Understanding the 1956 British Political Context
When Frank Cousins became Secretary of Transport Workers in 1956, Hugh Gaitskell, as the leader of the Labour Party, could not rely on votes from B) the trade unions. This is due to the fact that the trade unions had significant influence within the Labour Party, and individuals like Frank Cousins, who represented these unions, held substantial sway over the voting preferences of their members. Therefore, any actions or changes in leadership within the trade unions could have a direct impact on the support for the Labour Party leadership.
The situation within the Labour Party during the 1950s was complex. Different factions within the party, such as the Bevanites and those aligned more closely with Gaitskell, had their own agendas and sources of support. Trade unions, being a powerful force in British politics at the time, especially regarding the Labour Party, could shift the balance of power through their voting decisions at party conferences and in internal elections.