LONDON — Counterterrorism officers thwarted a terrorist attack targeting the British prime minister, Theresa May, prosecutors said when two suspects in their early 20s appeared in court on Wednesday.
Word of the planned attack coincided with what the authorities have depicted as mounting concern about the intensity, scale, and pace of conspiracies by violent extremists.
There have been five terrorist attacks in Britain this year alone, killing dozens of people in total. An official report on Tuesday said the worst of those assaults — at a concert by the pop star Ariana Grande in Manchester in May — might have been averted “had the cards fallen differently.”
The planned attack on May was to begin with a bombing of the security gates that protect 10 Downing St. — the home and office of British prime ministers — as a prelude to an attempt to stab her to death, prosecutors said.
Two suspects — Naa’imur Zakariyah Rahman, 20, and Mohammed Aqib Imran, 21 — were arrested Nov. 28. Rahman, a resident of north London, is accused of planning the bombing and knife attack. Imran, from Birmingham in the English Midlands, is accused of preparing acts of terrorism by traveling to Libya to join the Islamic State militant group.
Mark Carroll, a prosecutor, told the Westminster Magistrates’ Court on Wednesday that Rahman had planned to set off explosives at the gates of 10 Downing Street. In the ensuing chaos, he hoped to gain access to May’s office and stage a “secondary attack” using “a suicide vest, pepper spray, and a knife.” His purpose was to “attack, kill, and cause explosions.”
The accused did not indicate how they would plead when the case went before a higher court at the Old Bailey, London’s central criminal court, on Dec. 20.
In Parliament on Tuesday, the home secretary, Amber Rudd, said 22 Islamist plots had been prevented in the past four years, nine of them since March, when an assailant in a sport utility vehicle mowed down pedestrians and stabbed a police officer outside Parliament. Five people died in that attack, including the assailant, a 52-year-old Briton, Khalid Masood.
In May, Salman Abedi, a 22-year-old Briton of Libyan descent, blew himself up outside the concert hall in Manchester, killing himself and 22 other people.
In June, three men — Khuram Shazad Butt, a British citizen born in Pakistan; Rachid Redouane, a failed asylum-seeker who said he was Moroccan or Libyan; and Youssef Zaghba, an Italian of Moroccan ancestry — drove a van into pedestrians on London Bridge and then used knives to attack people around the nearby Borough Market. Eleven people died, including the three assailants, who were shot by the police.
Later that month, a British man, Darren Osborne, drove a van into a crowd of worshippers outside Finsbury Park mosque in London. One man died soon afterward, and Osborne has been charged with murder.
On Tuesday, an official report into attacks in May and June said counterterrorism officers had misinterpreted two items of intelligence handed to them before the killings in Manchester. Abedi was not being actively investigated at the time of the attack, but the items of intelligence could have led to an inquiry had their “true significance been properly understood.”
Counterintelligence officers “got a great deal right,” the report said. “Particularly in the case of Manchester, they could have succeeded had the cards fallen differently.”
The report was written by David Anderson, a senior lawyer commissioned by May to examine counterterrorism efforts.
Separately, Scotland Yard said on Tuesday, “The UK is facing an intense threat from terrorism, one which is multidimensional, evolving rapidly and operating at a scale and pace we have not seen before.”
Counterterrorism specialists have said one source of concern is that Islamic State combatants may be returning to Britain after military defeats in Iraq and Syria. Rudd said on Tuesday that Britain’s security services were embroiled in more than 500 investigations involving more than 3,000 people.