MI5 chief Sir Ken McCallum has warned that the United Kingdom now faces more complex and severe security threats than it did in 2001, when the 9/11 attacks shocked the world. Writing in an exclusive opinion piece for The Independent on the 25th anniversary of 9/11, McCallum said the country is dealing with both traditional terrorism and new strategic threats from powerful nations like Russia and China. He described this dual challenge as "the worst of both worlds," comparing the state actors to "dragons" and radical Islamic extremists to "snakes." McCallum emphasized that the UK’s current national security threat level is at "severe," the second-highest category, meaning an attack is highly likely. He noted that after the 9/11 attacks, a global effort was needed to weaken al-Qaeda, which has since been significantly diminished. However, new challenges have emerged, including state-sponsored aggression and cyber threats, which require updated strategies and legal frameworks to address. The MI5 chief called for a "shared national endeavour" involving not just the government, but also businesses, universities, and the public. He cited support from other experts, including former MI6 head Sir Alex Younger and former White House adviser Fiona Hill, who argue that the UK must prepare for a wide range of potential threats. This includes Russia’s hybrid warfare tactics and China’s growing influence over global trade and resources, which have increased the need for a coordinated national response. McCallum highlighted that many of the UK’s critical infrastructure and systems are now managed by the private sector, making collaboration between government, industry, and academia essential to address vulnerabilities. He stressed the need for new laws and intelligence techniques to combat state-backed aggression, such as cyber attacks on power stations or covert interference in democratic processes. He urged the country to focus not on whether an attack will happen, but on how to prepare for it when it does. In closing, McCallum paid tribute to the victims of 9/11, saying the UK owes them more than just remembrance. He called for the nation to build resilience and adaptability to face future security challenges, emphasizing that preparation and courage are essential to withstand the next crisis.