What exactly was so offensive about Thornberry's message? The subtext of this story is social class. Translating the episode at The Washington Post, Adam Taylor notes that the two flags hanging from the roof in the photo are St. George's Crosses, or English flags, while the third banner belongs to West Ham United, an East London soccer club. The flag of England is associated with far-right political groups like the English Defence League, which is often accused of racism (particularly Islamophobia) and xenophobia. West Ham, meanwhile, has a working-class following and a lingering reputation for hooliganism largely based on its fans' activities during the 1970s and 1980s.

The white van, meanwhile, brings to mind White Van Man, a British archetype for an outspoken, aggressive, self-employed tradesman (think a plumber or carpenter), a phrase alternately invoked with pride and derision. Here's how The New York Times described White Van Man in 2000:

In his hands he has a wheel; in his ears, rings; on his arms, tattoos; and in his heart, loathing for anyone he sees through his windshield. ... Once in the driver's seat, he considers red lights relative and his own authority absolute. His vocabulary is the kind represented in newspapers by asterisks, and the hand signals he uses to find his way are the kind that tell everyone else to get lost.

The layers of meaning in Thornberry's message don't end there. It mattered, for instance, that the tweet came from her. Thornberry represents the upscale Islington area of London and is a member of the Labour Party, which has recently been losing some of the working-class voters that used to make up its electoral base to the insurgent U.K. Independence Party. The right-wing UKIP, which opposes British membership in the European Union and takes a hard line on immigration, has been chipping away at the strength of Labour and Britain's other major party: the ruling Conservatives, or Tories. And it mattered that the tweet came this particular week from the Rochester area, where Mark Reckless, a Tory-turned-UKIP politician, was running for Parliament (he won). It mattered, moreover, that Thornberry had considered the scene worth photographing and tweeting in the first place.

Thornberry may have simply been marveling at the sight of "a house completely covered in flags," as she contends. (After all, as the journalist Shiv Malik has pointed out, the politician has a rather innocuous history of tweeting "a lot about buildings and stuff.")

But to many people the sum total of these factors suggested something different: that an out-of-touch, liberal elite from the capital was ridiculing and stigmatizing hard-working citizens. A Labour leader from Islington had snapped a picture of a modest, English flag-draped home with a white van out front. It was a scandal written and propagated almost entirely in code—and one that fit perfectly into the country's larger political narrative at the moment. Thornberry's actual intentions were beside the point.