Right-wing extremists? Anglican fanatics?
Maybe. But there is, as unlikely as it may be, one other possibility. The Islamic State issued this call in September 2014:
So O muwahhid, do not let this battle pass you by wherever you may be. You must strike the soldiers, patrons, and troops of the tawaghit. Strike their police, security, and intelligence members, as well as their treacherous agents. Destroy their beds. Embitter their lives for them and busy them with themselves. If you can kill a disbelieving American or European — especially the spiteful and filthy French — or an Australian, or a Canadian, or any other disbeliever from the disbelievers waging war, including the citizens of the countries that entered into a coalition against the Islamic State, then rely upon Allah, and kill him in any manner or way however it may be….If you are not able to find an IED or a bullet, then single out the disbelieving American, Frenchman, or any of their allies. Smash his head with a rock, or slaughter him with a knife, or run him over with your car, or throw him down from a high place, or choke him, or poison him….
“Buckingham Palace on lockdown: Two officers injured as police arrest driver in his twenties ‘armed with a MACHETE’ after he stops his car on the Mall – as terrified tourists look on,” by Abe Hawken, Mailonline, August 25, 2017:
Buckingham Palace is on lockdown after police arrested a man who allegedly attacked two officers while armed with a sword in front of frightened tourists.
Police stopped the man on the Mall at 8.35pm and discovered he was carrying a knife and two officers suffered ‘minor injuries’ to their arms when they detained him.
The man, who is in his 20s, was arrested on suspicion of grievous bodily harm and assault on police. Officers remain outside the world famous building this evening.
One witness described seeing the man wrestled from a car by police having apparently driven his vehicle towards them.
Kiana Williamson said: ‘We turned up and there was one police van and one car, there was also a civilian’s car that had veered towards the police car.
‘They were trying to get the man out of the car, shouting, more police were arriving on to the scene and the man was fighting back.
‘I saw one injured policeman with an injury to his arm although it didn’t look severe. He was being tended to by another officer.
‘The man had been restrained and looked almost unconscious by the side of the road.
‘I didn’t see the car driving but the car had been left at the side of the road and an eye witness had said that he had driven towards the police car.’
The whole encounter lasted around one minute, she added.
Social media users suggested the alleged attacker was carrying a sword – while others said he was holding a machete.
The Metropolitan Police said it was too early to know whether the incident was terror related….