The terrorist organisation Islamic State (Isis) is plotting a chemical weapons attack against Britain, the national security minister has warned.
Ben Wallace, Minister of State for Security and former Army Commander, said that Britain's intelligence and defence communities were planning for the possibility of a "mass casualty" attack on home soil involving chemical agents. He also expressed his fear that IS's territorial losses in Iraq and Syria may encourage its members to commit further atrocities in Europe.
He told the Sunday Times: "They [IS] have no moral objection to using chemical weapons against populations, and if they could, they would in this country. The casualty figures that could be involved would be everybody's worst fear."
"We have certainly seen reports of them using it [chemical weapons] in Syria and Iraq [and] we have certainly seen aspirations for it in Europe," he added.
It is estimated that around 800 Britons travelled to Syria to fight in its civil war. Roughly half of them are thought to have returned home.
Wallace said: "The insider threat, as we would call it, is real and it can be exploited and there are people trying to do that as we speak. If it's hard to get in the front door, then what you try and do is get someone on the inside. There are traitors. We have to be on our guard for the enemy within."
The current threat level for international terrorism in the UK is "severe", meaning an attack is highly likely. It was upgraded from "substantial" over two year's ago.
2016 was marred by terrorist attacks in European capital cities, but Britain was not struck by any terror attacks. However, British intelligence chiefs claim that several major terrorist attacks have been foiled over the last few years.
Wallace said: "The big concern is if Mosul collapses and all the other bases of [IS] collapse. We know there are a significant number of [Britons] fighting for IS in Syria. They will probably want to come home. There will also be those people who wanted to go out there but no longer can get there. Their frustration may boil over."
Wallace pointed to February's arrest of an IS cell in Morocco as proof the terror group's aims to carry out a chemical weapon attack: "Moroccan authorities dismantled a cell involving chemical weapons. They recovered toxic chemical and biological substances and a large stock of fertiliser. The substances found could have been used to produce homemade explosives and could have been transformed into a deadly toxin."