What's in a picture?

Further to my recent post on the perils of Twitter, another British politician has come a cropper because of a tweet. This time the victim (or villain, depending on your take) is Emily Thornberry, who tweeted a photo of a house displaying large St George’s flags (i.e. the English flag) and with a white van parked outside. The context of this is a little complicated to understand outside of England so I will try to summarise it. The house that was pictured is in the constituency of Rochester a