LONDON -- Britain on Monday marked the 20th anniversary of the 2005 London bombings that killed 52 people and injured over 700, with ceremonies, remembrance, and renewed focus on counterterrorism.

At 8:50 am(0750 GMT), the time the first bomb exploded, Prime Minister Keir Starmer and London Mayor Sadiq Khan laid wreaths at Hyde Park's memorial, with King Charles III praising acts of courage and compassion from that day.

Experts like Naomi Davis-Crane, a former counterterrorism analyst, warned of ongoing threats, especially from lone actors radicalized online. She stressed the need for vigilance, better victim support, and stricter control of extremist content on social media.

"There is a melancholy, and just a question as to when it will happen again — because it will happen again," she told Xinhua.

While the 7/7 attacks were carried out by four British nationals radicalized by al-Qaeda ideology, more recent incidents — including the 2017 Manchester Arena bombing and the 2021 explosion outside Liverpool Women's Hospital — reflect an emerging pattern of lone actors radicalized online.

The case of Southport murderer Axel Rudakubana may further illustrate how radicalization has increasingly moved online.

"A significant number of counterterrorist authorities during the last 20 years have realized the need to manage content that people are consuming via social media," said Davis-Crane.

"The social media platforms themselves have to identify and remove the content, and there is a responsibility on governments to legislate in this field," she added.

"Terrorism will impact every individual in a very different way, and the support needs will potentially last a lifetime," she said.