Complex sentence: Before his retirement in 1947, he proposed political reforms that would have allowed Hong Kong people to choose their own legislative council, which would handle every-day affairs and whose decisions would be immune to veto, even that of the governor himself.
Split into simpler sentences: Before his retirement in 1947, he proposed political reforms that would have allowed Hong Kong people to choose their own Legislative Council. He envisaged that the new Council would handle every-day affairs and that its decisions would be immune to veto, even to that of the Governor himself.