London police simulated the hijacking of a tourist boat on the River Thames on Sunday as part of training for a possible terror attack.
The Metropolitan Police said more than 200 police officers and staff took part in the exercise and involved other organizations, including the fire brigade, ambulance service and coastguard.
"The scenario involved a group of terrorists hijacking a passenger pleasure boat on the Thames and taking a number of hostages, to travel up the Thames to central London to carry out a terrorist attack," the Met Police said in a statement, according to a Reuters report.
"It was designed to test the response and command-and-control protocols of emergency services, working with maritime partners, in dealing with this kind of situation in a marine environment."
The Met said the scenario was not based on any specific intelligence, but last year an independent review of London's preparedness to respond to a terrorist attack, ordered by the mayor, recommended strengthening security measures on the river.
Britain's terrorism threat level is at "severe," which means an attack is deemed "highly likely."