Scotland Yard has stressed it is not aware of any specific threat to London, following the circulation of e-mails claiming another attack is imminent.
Police said they were aware of hoax e-mails being circulated
One hoax e-mail seen by the BBC claimed police were set to tell Londoners to avoid the Tube "at all costs".
But the Metropolitan Police said, while extra patrols were in place around London, "we are not aware of any specific threat at this time".
There had been "quite a few" inquiries about the e-mails, a spokeswoman said.
In a statement, Scotland Yard said: "Following the attacks of 7 July, extra policing patrols have been put in place across London, with officers from the MPS, City of London Police and British Transport Police providing visible reassurance, advice and support, and also to act as a deterrent.
"All police forces are reviewing their own counter-terrorist plans, undertaking community assessments and considering appropriate extra patrols in potentially vulnerable areas and transport hubs."
Police have advised the public to "remain alert and vigilant" and to call the anti-terrorist hotline on 0800 789 321 if they notice anything suspicious.