The jihadi group says the perpetrator who killed four in Westminster was responding to its call for attacks. Is this an opportunistic claim? 

ISIS on Thursday claimed that the man who killed four in Wednesday's terror attack at Britain's Parliament - named by police as Khalid Masood, 52 - was a "soldier of the caliphate."

In an online statement issued by ISIS' Amaq news agency, the group claimed credit for the assault, saying it was in response to ISIS' calls for attacks against countries involved in operations against the group. Publishing its claim before police named the perpetrator, ISIS provided no details about his identity. 

However, claiming responsibility for attacks such as the one on Parliament yesterday cannot be taken as evidence for direct ISIS involvement, or even for the perpetrator being ISIS-inspired. The group failed to provide further details other than those already circulated in mainstream media, and the idea that the attack was a response to ISIS' calls still cannot be substantiated. The group has long urged supporters to attack the West, but the scope of such calls makes it possible for ISIS to claim any incidents as its own, whether or not there is any direct or indirect involvement.

Chatter on jihadi accounts online yesterday indicated that ISIS supporters believed the attack was an Islamist extremist one. The terror threat in the UK has been 'severe' (its second highest level) since 2014, and multiple global jihadi groups have called for violence on the capital. 

ISIS sympathisers yesterday praised the violence as "blood with blood," due to British involvement in the offensive to retake Mosul from the jihadi group, according to terrorism researcher Rita Katz. On Wednesday night, the Metropolitan Police said they think they know who the perpetrator was, and suspect that he was inspired by international and Islamist-related terrorism.

Four people were killed in Wednesday's assault, including a police officer, and dozens wounded in and around the Palace of Westminster. The attacker was shot dead by police. Reports indicate that the perpetrator rammed into pedestrians on Westminster Bridge in a car, before running through the gates, and stabbing a policeman. In a statement, the Prime Minister said that he was British-born and known to security services. He was investigated by MI5 some years ago in relation to violent extremism.

In November 2016, the Director General of MI5, Andrew Parker, said that there would be a successful attack in the UK at some stage. In a speech in March 2017, Mark Rowley, the UK's most senior counter-terrorism officer, said that Britain's security services have foiled 13 terrorist plots in Britain since 2013, and that at any one time the British security services have 500 live counter-terror investigations. 

The extremist threat throughout Europe is severe. Between March and December 2016 there were at least 320 extremist arrests in 16 countries throughout Europe. Today marks the first anniversary of the Brussels attacks on an airport and a metro station, and ISIS in particular has called for its supporters in the West to carry out attacks using "whatever means they can." In April 2016, an ISIS propaganda video stated, "If it was Paris yesterday, and today in Brussels, Allah knows where it will be tomorrow. Maybe it will be in London or Berlin or Rome." This followed a September 2014 statement calling on the group's supporters in the West to "run [the enemy] over in your car."

It is not only ISIS calling for such things. In 2010, al-Qaeda's Yemeni branch (AQAP) ran an article in its English-language magazine calling the pick-up truck a "mowing machine... to mow down the enemies of Allah." 

Salafi-jihadi ideology is deeply opposed to democracy, which it regards as polytheism (shirk), as jihadis believe it gives authority to the people that properly belongs only to God. The attacker responsible for an assault on the Canadian Parliament in October 2014 made a video calling on the West to “stop occupying and killing the righteous of us who are trying to bring back religious law in our countries.”

Last year, there were at least two other Islamist attacks in Britain. In March 2016, an individual from Bradford travelled to Glasgow to murder an Ahmadi shopkeeper for supposed blasphemy. In February 2016, a Sufi leader was murdered by two ISIS supporters for supposedly practicing black magic.