Complex sentence: The purchase tax on new cars was reduced by 25 percent on 15 April 1953 (from 66⅔ percent to 50 per cent), which triggered a surge in demand for new cars on the UK market.
Split into simpler sentences: The purchase tax on new cars was reduced by 25% on 15 April 1953 (from 66⅔% to 50%). That triggered a surge in demand for new cars on the UK market.