Final answer:
In 1959, Hugh Gaitskell faced opposition from the left-wing members and trade unionists of the Labour Party when he tried to renounce clause 4, which advocated for the nationalization of industry.
Step-by-step explanation:
When Hugh Gaitskell, as the leader of the Labour Party, attempted to renounce clause 4 of the party's constitution in 1959, he faced condemnation from two significant groups within the party. These were B) The left and the trade unionists. The left-wing members were ideologically committed to the clause, which called for the nationalization of industry, as it was a fundamental part of the socialist principles of the party. Trade unionists also opposed the change, viewing nationalization as a means of protecting workers' interests. Hence, Gaitskell's efforts to modernize the party by moving away from this commitment to public ownership met with substantial internal opposition, revealing the deep divisions within the Labour Party at the time.