The UK's National Counter Terrorism Security Office told companies on Monday that they need to prepare their employees for the "full range" of terrorist attacks, just days after seven people were killed on and near the London Bridge.

"Following the attack in London Bridge, it is important that businesses remind their staff to stay alert and vigilant," the office wrote in a public memo. "The tragic events this year remind us that attacks can occur at any time or place without warning."

"Businesses are encouraged to review their security plans to ensure that the measures they should already have in place, are current and have been recently tested to ensure staff are prepared and confident," it added.

It noted that the London Bridge attack involved a vehicle and bladed weapons, and said companies need to be ready for anything, including improvised explosive devices.

"The public can expect to see additional police – both armed and unarmed officers – across London," it said. "In response to the ongoing threat the public will see an increased policing and security presence across the country at key sites, such as train stations and other crowded places to help protect communities."

The memo offered a range of advice to citizens, including how to stay safe during an attack, how to patrol areas and response to suspicious behavior, and the importance of keeping first aid kits up to date.

Prime Minister Theresa May said after the Saturday attack that she would keep the terrorist threat level at " severe" in anticipation of more possible attacks.