Detectives investigating extremist Islamist terrorism have arrested a 31-year-old man.
Scotland Yard said the suspect was held at a business address in south London just after 5pm on Tuesday.
He was detained under the Terrorism Act on suspicion of "being involved in the commission, preparation or instigation of acts of terrorism".
He was taken to a central London police station and remains in custody, while officers are searching a residential address in south London.
A Metropolitan Police spokesman said: "The arrest is being linked to extremist Islamist terrorism."
Armed officers were present when the arrest was made. No shots were fired.
It comes at a time of unprecedented activity by counter-terrorism units around the UK.
Police are conducting hundreds of investigations and have been making arrests at a rate of around one a day.
Home Office figures released earlier this month revealed that there were a total of 315 terrorism-related arrests in the year ending September 2015 - a jump of more than a third in just a year.
It was the highest tally for a year to September on record.
The data also showed that the number of women and girls being detained more than doubled compared to the previous year.