Police in the City of London cordoned off several streets near St Paul’s Cathedral on Wednesday after finding what a spokeswoman called a suspicious vehicle.
The lockdown lasted about an hour before roads were reopened and the area declared safe.
Police have been on high alert in recent days after a “suspicious item” was found on an underground train near the Canary Wharf financial district last week, leading to the arrest of a teenager under terrorism laws.
Britain is on its second-highest alert level of “severe”, meaning an attack is considered highly likely.