Tensions in London remained high Tuesday as police investigated reports of a possible bomb on a double-decker bus that ended up being nothing more than a possible mechanical malfunction.

Authorities had sealed off a portion of central London (search) due to a suspect package on the bus but the suspicious package was also investigated and found to be harmless. The situation was made more intense by witnesses saying they saw smoke coming from the bus.

The fire prompted police to shut down some roads in central London for about an hour. After the fire was out, officials said they believe the bus had an engine problem.

The incident was the latest in a string of more than 150 security scares in London following the deadly coordinated July 7 bomb attacks on London's transit system as well as the failed July 21 bombing attempt.

A total of 37 arrests have now been made in the English investigation of the botched July 21 bombings. Of those, 17 are still in custody. That total does not include the suspect held in Rome.

Two men and a woman arrested in raids in Brighton on Sunday were released without charge Tuesday.

Four other men were held in the same raids and warrants for police to hold them until this Friday were granted today.