A mountain of cash on companies’ balance sheets has set the scene for a battle between chief executives, who want to spend the money on M&A, and shareholders, who would rather they paid the money back.

US investment-grade companies' cash levels, relative to their debt, are the highest they have been in two decades, according to research by Morgan Stanley. At 21%, they are two or three times as high as they were in the 1990s, and a third higher than they were in the middle of the 2000s. Anecdotally, the picture is the same elsewhere.