On Tuesday, Dave Smith, a London Twitter user, noticed an unusual black flag flying at Will Crooks estate on Poplar High Street, near Canary Wharf, London.

At the entrance to the public housing complex, between a Palestinian flag and signs supporting Gaza (not unusual sights in London), was a black flag with Arabic writing on it. This flag bore a remarkable similarity to those used by the Islamic State, the extremist militia currently causing chaos in Iraq, which you can see below. Could a jihadist flag be flying in Britain?

A member of the Islamic State waves the group's flag in Raqqah, Syria, on June 29. (Reuters)

On Wednesday evening, Rajeev Syal, a reporter from the Guardian, headed to the estate to investigate. "A group of about 20 Asian youths swore at Guardian journalists and told them to leave the area immediately," Syal reports. "One youth threatened to smash a camera." When someone asked whether the flag was that of the Islamic State, Syal reports that one local man responded: "So what if it is?"

Another journalist, Ted Jeory, suffered worse abuse when he visited the site. “F*** off Jews. We don’t want Jews here, f***k off Jews," Jeory, who isn't Jewish, recalls hearing as he was threatened by a crowd of teenagers.

The flag's appearance caused a stir in the United Kingdom. Michael Fallon, British defense secretary, said: "That is extremely inappropriate when British lives are at risk, particularly in terms of terrorism from the jihad." According to London's Evening Standard newspaper, the flag was later removed by a local nun.

There's nothing illegal about flying this flag, but the British seem especially worried. The country, which has a large Islamic minority, tends to be sympathetic to the Palestinian cause – one prominent politician resigned over the Gaza crisis this week. At the same time, it has reason to be concerned about Islamist groups like the Islamic State. One report from 2013 suggested that about 400 British citizens had gone to Syria to fight. Many are concerned that they may bring back extremist attitudes and pose a terror risk.

In reality, the Islamic State is no friend of Palestinian militant groups such as Hamas. The group, however, has been able to brand itself as the face of global Islamist resistance, edging out more established names like al-Qaeda in the process. It's a reminder of why many people in Europe and the United States find the Islamic State so scary, even when they are far away.