New British PM Theresa May
Britain's Prime Minister Theresa May arrives at 10 Downing Street, in central London July 13, 2016. Reuters/Paul Hackett

An alleged terror plot to kill UK Prime Minister Theresa May has been foiled by security services. Police supposedly believed that there was a plan to launch an improvised explosive device at Downing Street.

Sky News reported on Tuesday that Sky's Crime Correspondent Martin Brunt said that the alleged plot has been the latest terror plot that police have foiled this year. The supposed plan to bomb Downing Street and assassinate May was said to have been uncovered through a joint operation between MI5 and police.

Prime ministers have long been targets of terrorists. Armed police officers and fortified gates protect Downing Street.

Security measures introduced in the 1970s were boosted in the 1980s. At that time, threats from Irish republican groups grew.

Details of the alleged Islamic extremist plot were set out to Cabinet members during a briefing by MI5 head Andrew Parker, who revealed on Tuesday that nine terror plots have been foiled by the British intelligence in the past 12 months. Britain’s official terrorist threat level is at severe. This means an attack is highly likely.

Terrorist offences

Two men have been charged with terrorist offences, according to police. Mohammed Aqib Imran, 21, and Naa'imur Zakariyah Rahman, 20, were arrested in raids. Both were arrested by counter-terrorism police last week. They were due to appear in a London court on Wednesday.

In March, Khalid Masood stabbed a policeman guarding Parliament. He also drove a car at pedestrians on Westminster Bridge, an attack that killed five people.

Twenty-two people died in May when suicide bomber Salman Ramadan Abed targeted the Manchester Arena. Opportunities to thwart the attack have been missed, according to an official report released on Tuesday.

MI5 and the police conducted internal reviews following attacks at Manchester, Westminster Bridge London Bridge and Finsbury Park. The attack at Parsons Green in September was not covered by the report.

Parker has warned that the Islamic State’s defeat in Syria did not end terrorist threat. Social media, he said, is being used to provoke terrorist attacks.

Technology companies Microsoft, Facebook, YouTube and Twitter have earlier announced they would start sharing digital fingerprints of videos they removed from their platforms for terrorism. The four big social media companies are part of a group called the Global Internet Forum to Counter Terrorism. May has called for international regulation to force tech companies to do more to keep extremists off their platforms.