Britain's top domestic intelligence officer has warned that Britain is under unprecedented threat from Islamist terrorists, and says that 20 plots have been foiled in the past four years, while future successful attacks are inevitable.
During a rare speech in central London, Mr Parker said: "No company wants to provide terrorists with explosive precursors, ..."
"In 2017, with all that has happened and much that has not, it is clear that we are contending with an intense United Kingdom terrorist threat from Islamist extremists", Parker said during a rare public speech.
Parker highlighted that the Islamist threat was operating at an unprecedented scale, noting there had been a "dramatic" rise in terror plots, which had become increasingly hard to detect. There have been a record number of terrorism-related arrests: "379 in the year to June", he said.
The UK has suffered five terror attacks this year, and he said MI5 staff had been "deeply affected" by them.
He said continental Europe has faced a similar surge, particularly in France, Belgium, Germany and Spain.
Speaking in London, Parker said the tempo of counter-terrorism operations was the highest he had seen in his 34-year career at MI5.
Some had then returned, often many years ago, and had been subject to risk assessment and at least 130 had been killed in conflict fighting for the Islamic State (ISIS) terror network.
He said MI5 is well-equipped to cope with the deepening threat, with its ranks set to grow from 4,000 to 5,000 over the next few years.
He drew attention to the fact that that terrorist attacks "can sometimes accelerate from inception through planning to action in just a handful of days", something that "can give us a smaller window to intervene". "Nor would we want to live in a country that was like that". "And communications providers don't want to provide the means of terrorist planning, beyond the sight of MI5", said Parker.