A security source says terrorists linked with the Islamic State are being closely monitored by security services across the London, West Midlands, and Manchester areas.
The source says more than 3,000 British militants have advanced in the United Kingdom, preparing to launch several deadly attacks that could bring chaos to civilians and even the military forces.
According to Mirror, security sources say thousands of terror group suspects are based in Britain areas and are being monitored by M15 and other anti-terror police. While the vast majority are residing in London, many of the suspects are also believed to be living in Manchester and the West Midlands.
Due to the rise of the biggest terror group worldwide, the number of homegrown jihadists who are willing to execute attacks in Britain has significantly risen in the past two years.
Director general of M15 Andrew Parker said in an interview with BBC Radio that although six attempted attacks have been foiled by Britain's forces, it is still facing its most trifling threat since the 9/11 attacks on the United States.
Parker pointed out that most of the people trying to get into the terrorist group and are now extremists have been born and raised in Britain, adding that "they have come through our education system, and have nonetheless concluded that the country — their home country and the country of their birth — is their enemy."
August of last year has raised its terrorist level threat to "severe," which is the second highest category and also indicates that militant attacks are very likely expected and prepared for by the government.
Authorities say the possibilities are largely due to the dangers posed by ISIS fighters and the hundred other Britons who have willingly laid their lives on the line for the terror group.
Meanwhile, several reports state that the Islamic State is slowly crumbling since Syria and Iraq have estimated that about 8,000 of the terrorists have been wiped out by the US-led air drone strikes.
On the other hand, Britain remains threatened due to the group's ideologies, plus the report that thousands of homegrown IS members are lurking on the streets.