Final answer:
John Maynard Keynes was the British economist who criticized laissez-faire economics and advocated for the use of fiscal policy to manage the economy, especially during downturns.
Step-by-step explanation:
The British economist who criticized laissez-faire economics and advocated economic management through fiscal policy was John Maynard Keynes. He believed that during economic downturns, the government should play an interventionist role, increasing spending and offering tax breaks to mitigate the effects of recessions and depressions. Conversely, in prosperous times, Keynes suggested the government should cut spending and increase taxes to control inflation. His contribution to economics also included the idea that economics is a method of thinking, helping individuals to draw correct conclusions.
Keynes argued that the government should play a more active role in the economy during recessions and depressions by implementing fiscal and monetary measures, such as increased spending and tax breaks, to stimulate economic growth and employment. His ideas were revolutionary at the time and have greatly influenced modern views of macroeconomics and economic policies.