Counter-terrorism police arrested seven people over the past 48 hours on suspicion of plotting an arson attack on a Jewish community venue in London, bringing the total number of detentions in the probe to 23.

An eighth arrest occurred overnight when officers detained a 39-year-old man at an address in Ealing under section 41 of the Terrorism Act 2000. Among the seven latest suspects were three men aged 24, 25, and 26 arrested in Harpenden, Hertfordshire, shortly after 9 p.m. on Sunday; those three have been released on bail. A 25-year-old man was arrested in Stevenage, Hertfordshire, while a 26-year-old man and two women aged 50 and 59 were detained in a car near Birmingham; those four remain in custody at a central London police station, along with the Ealing suspect.

The arrests form part of a proactive investigation into an alleged conspiracy to commit arson, Counter Terrorism Policing said. A search continues at a premises in East London. Thirteen individuals are now in custody or on bail pending further inquiries, and eight people have been charged with arson-related offenses.

Deputy Assistant Commissioner Vicki Evans, senior national coordinator for Counter Terrorism Policing, said: "We’ve made very clear that we will be relentless in our pursuit of anyone involved in carrying out or planning these arson attacks." She warned potential proxies that "the stakes are high, and it is absolutely not worth the risk," noting possible use of people paid to commit crimes.

The plot connects to a series of attacks on Jewish sites in northwest London since late March. On March 23, four ambulances from the Jewish charity Hatzola were destroyed by fire in Golders Green. Arson struck Finchley Reform Synagogue on April 15, followed by an ignited bag at a former Jewish charity building in Hendon on April 17 and Kenton United Synagogue in Harrow early on April 18, where a bottle of accelerant caused minor smoke damage. Other incidents include fires at bins outside a Barnet communal block and attacks on Persian media offices critical of Iran.

A pro-Iranian group, Harakat Ashab al-Yamin al-Islamia, has claimed responsibility online for several attacks, prompting inquiries into Iranian proxy involvement. Met Deputy Commissioner Matt Jukes described the incidents as part of a "modern hybrid war fought by proxies," with patterns suggesting cash-for-crime recruitment.

Earlier arrests include two teenagers, a 17-year-old boy and a 19-year-old man, held over the Kenton attack, contributing to the prior tally of 15 detentions and seven charges.

Security Minister Dan Jarvis called the attacks "completely abhorrent," vowing government support for Jewish communities. Chief Rabbi Ephraim Mirvis warned of a "sustained campaign of violence and intimidation" against British Jews.

Police have increased patrols around Jewish sites in northwest London to deter further incidents and reassure communities.