By the end of 1904, the Tariff Reform League's numerous branches were challenging the Conservative National Union. Chamberlain also attempted to secure the Tariff Reform League's representation inside Conservative Central Office. Balfour maintained his programme of retaliatory tariffs and attempted to minimise the obvious differences between Chamberlain and himself. Publicly, Chamberlain claimed that Balfour's stance was the precursor to a fuller policy of Imperial Preference. Now approaching seventy years of age, Chamberlain continued to campaign for tariff reform with zeal and energy. Reconciliation appeared imminent when Balfour agreed to a general election after the 1906 Colonial Conference, in which tariff reform would be discussed. However, threatened by backbench opposition, Balfour rescinded the agreement and demanded party unity. Chamberlain ignored this and intensified his campaign in November 1905, resulting directly in Balfour's resignation on 4 December.