The bombing that left 22 people dead at a Manchester concert hall on Monday is likely to again draw attention to the activities of the small minority of the UK's Muslim population that supports Islamist extremism.

Police named the bomber as 22-year-old Salman Abedi, who was born in Manchester and who has lived at several addresses in the city.

While police are not saying he was an Islamist, Islamic State has claimed responsibility for the bombing, a connection that has not been confirmed.

British authorities estimate around 3,000 people in the United Kingdom have the potential to carry out acts of terrorism, or attempt to join Islamist fighters in Syria, Iraq, Somalia, Libya or elsewhere. Among them are around 400 people who have returned from fighting for Islamic State in Syria and Iraq.

It is not yet known whether Abedi was on any of the watchlists. People on such lists cannot be arrested if they have not committed a crime.

Khalid Masood, 52, who killed five people next to the Houses of Parliament in London in March was a peripheral figure in a police investigation into Islamist extremists in 2010. By 2017, police said they had no evidence he was planning to do anything illegal, or that he had any connection to terrorist groups.

Masood, a convert to Islam, said via a Whatsapp message sent minutes before his rampage that he carried out his attack in retaliation against Western military action in the Middle East.

The fact that Masood's name was not on the list of 3,000 potential terrorists demonstrates the difficulty that authorities have in defending the public from random acts of terror.

Modern technology allows security services to monitor calls, emails, car journeys, bank transactions, internet browsing, and much else. But those who are serious about avoiding attention can use encryption and other ruses to disguise their electronic traffic. And they can avoid technology altogether by passing messages in person, using cash, and keeping their conspiracies simple and their associations limited. To follow such terrorists, the security services need to track them in person, which, to be done properly, requires teams of watchers working around the clock. The security services say they can only do this for high-risk suspects.

After a terrorist attack, there are often calls for suspects to be interned, or detained without trial. Allison Pearson, a newspaper columnist, tweeted on Tuesday: "We need a State of Emergency as France has. We need internment of thousands of terror suspects now to protect our children."

But most people realize that internment is likely to be counterproductive. It would risk damaging relations with the UK's 2.86 million Muslims because of the activities of a few hundred people who do not represent that community, which is exactly what the Islamist extremists would like to see happen.

The UK last used internment in 1971 in Northern Ireland against Irish republicans. The policy strengthened Irish republicans, rather than weakening them and prolonged and deepened the conflict, which continued until 1998.

Up to this year, the UK security services have been very successful in preventing attacks. The killings in Manchester and London were the first to have resulted in the death of more than one person since the 2005 London attacks that left 52 dead. Police and intelligence services, aided by the Muslim community and others, have foiled dozens of ambitious plots in recent years.

It has become very difficult to carry out acts of terrorism in the UK but the Manchester bombing raises major concerns.

The attacker in London used a hired car and a knife as his weapons, which made him more or less invisible to the authorities before he carried out his attack, but the Manchester bomber was able to collect bomb-making materials and know-how, things that have been closely watched since the days of the IRA.

The strength of the explosion, the inclusion of bolts in the bomb that maximized the carnage, and the fact that the bomber was able to smuggle the device into a relatively secure area, suggests a degree of skill in bomb-making. The security services will be racing to ensure a master bomb-maker, like Najim Laachraoui, who made the bombs used in the Brussels and Paris attacks, is not at large, with a supply of suicide bombers ready to wreak carnage.