LONDON (CNN) -- Britain's police swung into action Thursday as two separate incidents, one involving a security scare on a bus and the other six terror arrests, pointed to the heightened state of alert ahead of the London Olympic Games.

Security is a central concern for UK authorities and the organizers of the Olympics, which start in three weeks.

After launching a major response to the security alert on the bus, which led armed officers to close a major motorway, police in Staffordshire concluded the incident was not terror-related.

But its officers responded "swiftly and proportionately" to credible information from a concerned member of the public, a Staffordshire police statement said.

"We can now confirm that, whilst this was a genuine security alert, the significant concerns reported to us were unfounded," the statement said. "The information received concerned a report of vapor escaping from a bag which on investigation turned out to be a health improvement aid for smokers."

Hours earlier, police in London arrested five men and a woman on terror charges, although they said the operation was not related to the Olympics.

The six, aged from 18 to 30, were all arrested on suspicion of the commission, preparation or instigation of acts of terrorism and are being questioned, London's Metropolitan Police said. Officers searched homes in east, west and north London as well as business premises in east London.

One of the men arrested had worked from 2007 to 2009 as a police community support officer for the Met Police, the force said in a statement, and "was not deployed in a specialist or sensitive role." Police community support officers are members of staff who work alongside the regular police force, mostly to tackle local anti-social behavior and low level issues.

The operation in London is not linked to the Olympic and Paralympic Games, the police said.

Additional security measures will be in place in London and elsewhere during the Olympics.

They include the siting of missile defense systems around the capital and fighter jets on standby at air bases close to London. Police and intelligence agencies have also stepped up monitoring efforts.

Thursday's dramatic closure of the busy M6 Toll motorway, near Birmingham, had many hallmarks of a response to a potential terror threat and could be seen as a sign that police are taking no chances.

Armed police, firefighters and military bomb disposal units raced to the scene as passengers were evacuated from the bus, which had pulled over near the town of Lichfield. Police in Britain are not usually armed when they respond to incidents.

Passengers were lined up on the tarmac for questioning, and their luggage and the vehicle searched, before police confirmed that there was no terror threat and that no one was considered a suspect.

"Our utmost priority was the safety and security of those people on the coach and those traveling on the motorway," the force said.

The 48 passengers who were on the bus from the northwestern city of Preston to London are now being taken on to their planned destination, a spokeswoman for Megabus said.

"We would like to thank our customers for their patience and understanding during today's police operation, which followed concerns raised by a passenger during the journey," a statement from the bus operator said.

"The safety and welfare of our passengers and our staff is our absolute priority."

The bus has been moved and the highway has reopened, police said.

Government officials from Washington to London insist there are no known specific or credible terror threats tied to the Olympic. Nonetheless, authorities on both sides of the Atlantic are urging vigilance.

The Metropolitan Police is leading the "largest peacetime operation" seen in the United Kingdom as it seeks to keep the public safe, it said, with up to 9,500 police officers from London and elsewhere to be deployed on the busiest days of the Olympics.

As a result, London's residents and its visitors can expect to see a large police presence on the streets and airport-style security at Olympic venues.

CNN's Laura Perez Maestro, Claudia Rebaza, Laura Smith-Spark and Nic Robertson contributed to this report.