British Transport Police (BTP) should be given more resources to boost safety on London Underground, a security expert has said.
Deploying more officers should be prioritised over installing check points at Tube stations, according to Will Geddes, founder of private security firm International Corporate Protection.
He told the Press Association that introducing airport-style barriers "is not necessarily going to be a solution" because of the huge number of passengers using the network.
"The terrorist is always going to look for the path of least resistance," he said.
"If you've got additional checkpoints on the exterior of the airport or the Tube station, you create a choke point, you create a build-up of individuals which could be exploited.
"What will hopefully happen is BTP will be given more resources to continue initiatives they're currently running, where they have periodic sweeps by plain-clothed covert officers who are carrying out hostile surveillance detection.
"They're ideally picking up on individuals who might be planning to do something or are in the right position to be able to react as quickly as possible should something happen."
Around 700 uniformed BTP personnel are deployed on the Tube and Docklands Light Railway, part of 3,000 across the capital's transport network.
Mr Geddes said passengers play a "critical part" in combating terrorism.
"It couldn't be more true, especially on the Underground," he said.
"You've seen the posters, you've heard the announcements. If you see an unattended package, or something else suspicious, report it.
"It's really, really key. The general public are the eyes and ears on the ground."
A bomb blast tore through an underground train deep in St Petersburg, Russia, on April 3, killing 11 people.
About 100 people were killed when two bombs were detonated outside Ankara train station in Turkey in October 2015.