Which one of the following factors constitutes the best safeguard of liberty in a liberal democracy?

A committed judiciary, meaning one aligned with government policies, would be unlikely to challenge governmental actions and thus unable to effectively protect liberty. Therefore, option (a) is incorrect.

Centralization of power, where decision-making is concentrated at the top, fosters authoritarianism and restricts liberty. Thus, option (b) is also incorrect.

While an elected government is representative and should protect liberty, it isn't the best safeguard.

Separation of powers among the executive, legislature, and judiciary provides checks and balances, preventing any single branch from becoming too powerful. This system is the strongest safeguard against authoritarianism and the best protector of liberty.

Hence, option (d) is the correct answer.