The first incident began in the early early morning hours Friday, near London's famous Piccadilly Circus. An ambulance crew near an area nightclub noticed smoke coming from an abandoned car and summoned police. Police found at least one gas cylinder inside the vehicle, and the bomb squad was called in.
In a statement, London police said officers discovered what they called "a potentially viable explosive device" that they then defused.
Anti-terrorist and forensic teams closely examined the vehicle before it was removed from the scene.
Traffic was disrupted in parts of west London as investigators gathered evidence.
On Friday, new Prime Minister Gordon Brown chaired an emergency security meeting where the latest details were discussed.
"The first duty of a government is the security of the people and as the police and security services have said on so many occasions, we face a serious and continued security threat to our country," said Brown.
"We should allow the police to investigate this incident and then report to us. But this incident does recall the need for us to be vigilant at all times and the public to be alert at any potential incidents," he added.
Next week, Britain marks the second anniversary of July 7 2005 London transit bombings, in which four Muslim suicide bombers set off explosions that killed 52 bus and subway passengers and the bombers themselves.