Seven of the arrests were made within the past 48 hours as part of a probe into a suspected conspiracy to commit arson, the police statement said.
While they did not identify a specific venue, police said an intended target was connected to the Jewish community.
The arrests come as United Kingdom police have been investigating a string of attacks on Jewish-linked sites in the capital, part of a wider rise in threats and criminal activity since the outbreak of the Israel-Hamas war in the Gaza Strip in October 2023.
UK security officials have warned that Iran has sought to use criminal proxies to carry out hostile activity in the UK, and the pro-Iranian group Harakat Ashab al-Yamin al-Islamiyya has claimed some of the latest attacks on social media.
Police made no connection between the group and the latest arrests.
In the latest operations, police said detectives had arrested three men aged 24, 25 and 26 in Harpenden, north of London, on Sunday evening before releasing them on bail.
On Monday, a 25-year-old man had been arrested in Stevenage, north of London, while a 26-year-old and two women aged 50 and 59 had been arrested in a vehicle near the central English city of Birmingham and taken to a London police station, where they remained in custody.
On Tuesday morning, officers arrested a 39-year-old man at an address in west London under the UK's Terrorism Act 2000.
Police said the arrest had been linked to an investigation after jars containing a non-hazardous substance had been found in Kensington Gardens in central London last week.
Searches were continuing at a premises in east London, officers added.
Separately, a 17-year-old boy pleaded guilty on Tuesday to arson not endangering life, police said, following an attack on a synagogue in north London over the weekend.
The fire caused minor damage and no injuries.
Since an attack last month on several ambulances belonging to a Jewish charity, counter-terrorism police said they had arrested 23 people.
