Tear stricken children at the Holt School in Wokingham held hands, lit candles and laid flowers to remember “Sir”, after James Furlong, 36, the head of history, government and politics, was named as one of three victims of the Reading knife attack.

As the school’s flag was flown at half mast, co-headteachers Anne Kennedy and Katie Pearce said “he truly inspired everyone he taught”, while parents, Gary and Janet, described him as “the best son, brother, uncle and partner you could wish for. We are thankful for the memories he gave us all. We will never forget him and he will live in our hearts forever”.

Former pupil Molly Collins, who left the school in 2017, put it simply: “He was such a loved teacher. Anything that was boring, anything you didn’t find interesting, he would make it interesting.”

Furlong’s friend, Joe Ritchie-Bennett,39, an American who had lived in Britain since coming from Philadelphia in Pennsylvania 15 years ago and worked for a Dutch pharmaceutical, was named as the second victim.

In America, his brother, Robert Ritchie, a captain in the Philadelphia police force, recalled, “We rode bikes together every day, our family is heartbroken,” while their father, also called Robert, could only say: “I absolutely love my son with all of my heart and all of my soul.”

The home secretary Priti Patel, who placed flowers near the scene of the killings in Reading and was to address the Commons, spoke of lessons to be learnt.

She said: “There is extensive work that’s taking place, yes, with the police but obviously now with CT (counter-terrorism) police as well, and the intelligence community and all aspects of policing.

“We’ve got a lot of information to gather, we have to look at all aspects as to what happened on Saturday, the individual that’s in custody as well, to ensure that, yes, justice is served.

“But, also, we make sure that we learn the lessons from what has happened over the weekend to prevent anything like this from happening again.”

She added: “The security services have records on thousands of people, and rightly so, subjects of interest, people of concern.”

The suspect, Khairi Saadallah, a 25-year-old Libyan — he is being held under “Section 41 of the Terrorism Act” — has found an odd way to show his gratitude to Britain which granted him asylum for five years in 2018. He said he needed shelter after fleeing the deadly civil war Libya.

But then he launched immediately into a life of crime. Saadallah was jailed for 25 months and 20 days for various non-terror-related offences dating back to November 2018.

The offences included racially aggravated common assault — after he called a police officer a “slave” and spat in her face — carrying a sharp article and assaulting an emergency worker.

Saadallah, who had lived at Basingstoke Road in Reading, had his overall sentence reduced to 17 months and 20 days through the Court of Appeal in March this year.

Saadallah left Her Majesty’s Prison Bullingdon, Oxfordshire, 17 days ago after serving less than half of his sentence.

Last year he came to the attention of British intelligence because there was a suggestion he wanted to go to Syria for the purposes of terrorism but he was not considered to be a serious threat.

Sir Mark Rowley, a former head of UK counter terrorism at Scotland Yard – he was Neil Basu’s predecessor – revealed on Monday that the number of people thought capable of launching a terror attack stands at about 40,000. But only a fraction of that number can be monitored round the clock.

“What you end up with operationally are about 3,000 people under investigation at one stage,” he explained. “But there are 40,000 people whose names have touched the system. And in that 40,000 are lots of volatile people who dip in and out of interests in extreme ideology, and to spot one of those who is going to go from a casual interest into a determined attacker, which can happen in a matter of days, is the most wicked problem that the services face.”