Britain's migrant crisis is making a terror attack more likely, the head of MI5 has warned. Sir Ken McCallum admitted intelligence officers have seen an increase in “anti-immigration and anti-Muslim” grievances “tipping into terrorist intent”. He said MI5 has foiled plots to attack mosques and “venues connected to immigration and asylum”.
Threat level raised to SEVERE
Britain's top intelligence officer said: "For the first time in almost five years, JTAC recently returned the UK terrorism threat level to SEVERE, meaning an attack is highly likely."
Sir Ken's intervention will prompt renewed focus on the disastrous impact of the failure to control Britain's borders.
Extreme right-wing terrorism driving increase
He said: "While the threat level change reflects the whole of the terrorist threat, the recent increase was driven in significant part by Extreme Right-Wing Terrorism."
"This is a complex landscape, with many subcultures. Over the last year, the most marked trend has been an increase in cases where extremists of anti-immigration and anti-Muslim grievance are tipping into terrorist intent; we’ve dealt, for example, with would-be terrorists aspiring to attack mosques and venues connected to immigration and asylum."
MI5, Sir Ken said, is still foiling Islamist attempts “to carry out mass casualty attacks in the UK”. He said: "Determined efforts have degraded the leadership of Islamic State, but Al-Qaeda and Islamic State continue to direct and inspire attacks. Three Islamist extremists were convicted in February for planning to use automatic weapons against the Jewish community in Manchester."
Radicalised young people and online propaganda
Britain’s top intelligence officer warned extreme right-wing terrorism continues to “skew” young people radicalised by online propaganda. He said: "A few months ago, MI5 was investigating a radicalised extreme right-wing 13-year-old here in the UK. Believe me, we wish we didn’t have to. But that investigation generated insight that enabled one of our international partners to prevent a lethal attack on their soil."
He also mentioned the case of a 16-year-old from Inverclyde who was jailed for 10 years for plotting to attack an Islamic centre. Official figures show that in 2025, 39 people aged 17 and under were arrested in connection with counter terrorism investigations, and 40 the previous year.
National security front line and political warnings
Sir Ken warned Britain’s adversaries are trying to “manipulate how we feel”. He said: "In the era we’re now in, the cohesion and confidence of our communities has become a national security front line. Those who mean us harm are trying – often with a helping hand from polarising algorithms – to divide our communities and turn us against one another. The sharpest form this takes is lethal violence. We were all horrified by the murder of Ann Widdecombe in July. Sadly, the case is part of a concerning trend of violence targeted at political figures, religious or community groups and more."
Sir Ken added: "Authoritarian regimes also try to impose their will. They have forever sought to silence dissenting voices among their people, including in the UK. But these days they also invest in trying to distort and divide our society, weaponising whatever frictions they notice."
Reform UK leader Nigel Farage on Monday warned Labour is letting terrorists, serious criminals and dangerous sex offenders cross the Channel in small boats. Mr Farage vowed to regain control of the borders by shutting the asylum system for five years. He said: "What is happening is a national security emergency. We are letting terrorists come into the country. We are letting serious criminals come into the country. We're letting dangerous sex offenders into the country. And our primary purpose is to stop that from happening. We have got to be very, very careful about not letting any more of our enemies into the country."
