The City of London Police force was facing criticism last night after including the Occupy London demonstration in a letter warning businesses about potential terrorist threats.

The letter, a "Terrorism/Extremism Update", lists al-Qa'ida, the Colombian dissidents Farc, and Belarusian terrorists who bombed the Minsk underground. It also lists Occupy London under the heading "Domestic".

It states: "It is likely that activists aspire to identify other locations to occupy, especially those they identify with capitalism. City of London Police has received a number of hostile reconnaissance reports concerning individuals who would fit the anti-capitalist profile. All are asked to be vigilant regarding suspected reconnaissance, particularly around empty buildings."

An Occupy London spokesman said: "Activism is not a crime and the desire to participate in democratic decision-making should not be a cause for concern for the police in any free society.

“An institution that confuses active citizens with criminals and equates al-Qa'ida with efforts to reimagine the city is an institution in danger of losing its way."

A police source said the letter was authentic but was poorly worded and never meant to imply demonstrators posed a terrorist threat.