The Short Version
India was undeniably a massive and uniquely important source of wealth for the British Empire, but the specific claim that it was the "single largest source" requires an empire-wide comparative ranking that no credible source in the evidence actually provides. The large extraction figures cited ($45–$64.82 trillion) apply only to India and are methodologically contested; no comparable accounting exists for other colonies such as the Caribbean, South Africa, or Malaya. The claim is directionally plausible but presents an unproven superlative as established fact.