For most Americans, a trip to London means drinking a few pints and maybe taking a picture of one of those guards with the hats. For Paul Krugman, it means critiquing the entire direction of Britain's economic policy.

Krugman, the Nobel Prize-winning economist and left-leaning New York Times columnist, appeared on the BBC program "Newsnight" this Wednesday, jousting with two British deficit hawks over the U.K.'s austerity agenda.

The Brits -- venture capitalist Jon Moulton and Conservative Member of Parliament Andrea Leadsom -- argued that the British government has to reduce spending if the country is to dig itself out of the economic slump it's been in. Krugman countered that such a strategy could cause Britain's economy to implode -- since, he said, the public and private sectors need to circulate money to each other in order for anyone to prosper.

"We are not a household. We are an economy," said Krugman. "Your spending is my income, and my spending is your income."

As Krugman pointed out during the "Newsnight" segment, and later in a NYT column, the austerity question is one that extends beyond Great Britain. Eurozone countries are in the midst of their own austerity struggle right now, one whose effects have been felt most strongly in Greece, where government spending cuts have resulted in riots and strikes and boosted the political fortunes of the far-left, anti-austerity Syriza party.

And in the United States, economists and politicians are engaged in an ongoing debate over the best way to jump-start the lagging economy -- and here, too, Krugman has repeatedly counseled against the kind of major government spending cuts that conservative policymakers have championed.

Krugman's argument is that such cuts would cause a major contraction in the American economy, a point that even Mitt Romney, the presumptive Republican nominee for president, appeared to echo in an interview with Time a few days ago.