London descended into chaos on Tuesday afternoon after twin bomb scare sparked mass evacuation of thousands of people from buildings around BBC Broadcasting House and London Bridge.
Bomb squad detectives were rushed to the area around one of the city's busiest stations after a "suspicious package" was found in a nearby building.
It came just moments before staff working at BBC Broadcasting House was evacuated following a bomb scare.
Police put London Bridge underground station on lockdown and evacuated several buildings in Tooley Street, in the heart of London, after the suspicious object raised fears of a possible terrorist incident.
Sniffer dogs were seen being led into Counting House, which is the home of the charity Prostate Cancer UK, before police later declared the area safe.
In a separate incident, staff at the BBC headquarters - just a mile from Buckingham Palace - were affected as Portland Place was cordoned off because of reports of a ''suspicious vehicle''.
Great Portland Street was closed off and Regent Street blocked off.
Scotland Yard later confirmed the alert had been cancelled by 3.15 pm and that the vehicle was found to be non-suspicious.
Both security scares saw thousands of people evacuated from central London buildings in close proximity to suspicous items.
Britain remains on high terror alert, with special forces deployed on the streets of London.
The move is the biggest security response since the 2005 London bombings and comes after last month's Paris atrocities.
Earlier, office workers described the terrifying moment they were told to leave their buildings and head outside for an evacuation point near the iconic HMS Belfast on the River Thames.
Member of staff Gary Haines tweeted: "Update from London Bridge. Sniffer dogs in Counting House, home of @ProstateUK"
The police later tweeted that the event near London Bridge had been a false alarm.
The Metropolitan Police's local Southwark account wrote: "Counting House at Hays Galleria safe to return to. We really appreciate your patience and compliance with officer directions at the scene."
Helen Monaghan tweeted: "The amount of helicopters flying over London Bridge right now is insane."
The underground station was temporarily shut but Network Rail and Transport for London (TfL) both confirmed that the railway station above remained open throughout the scare.