How Lidl has used monopsony power to increase their market share

How much room is there for the "deep discounters" to drive market share still higher - perhaps to round 20 percent?

This article is great for understand how lean retailing helps to increase productive and where buying power (monopsony) gives the retailer an advantage in an age when real incomes have been squeezed.

But Aldi and Lidl themselves face growing competitive pressures especially if there is a scaled change in the cost, price and convenience of online food deliveries.