Police warning to Guy Fawkes-themed protesters attending Million Mask March

Thousands of people are expected to descend on central London for the Million Mask March.

Police have warned "masked criminals seeking to run amok" that they will be arrested if the protest turns violent.

Clad in Guy Fawkes masks, thousands of supporters of Anonymous, the anarchic hacking collective, are expected at the event on Saturday.

The annual protest is one of many similar marches held worldwide on November 5. Its agenda is broadly anti-capitalism and pro-civil liberty.

Last year's march saw ugly scenes as missiles and fireworks were thrown at police. Four officers and six police horses were injured.

More than 1,000 people are estimated to have taken part and there were more than 50 arrests.

Ahead of the event, Metropolitan Police Commander BJ Harrington said it was apparent that some only went along "intent on criminality".

He added: "Last year we saw participants causing criminal damage to public property, smashing the windows of businesses and attacking police officers all whilst harassing and intimidating families as they visited theatres, dined out or shopped in the West End.

"The public found this completely unacceptable. This was not peaceful protest by any measure. Those who chose to behave like this are not protesters, they are criminals, and they undermine the thousands of people who protest responsibly and safely in London every year.

"As we look ahead to this weekend, my message is simple: if you want to protest peacefully, that is your right and we want to work with you.

"If you commit criminal acts - that is not peaceful protest - and you are liable to be arrested."

However, protest organisers Million Mask March London appeared to be putting on a defiant front, posting on their Facebook page that "the police are not your friends".

In a press release, it called on "the Metropolitan Police to restrain from violence and their usual mob mentality".

Almost 20,000 people have said on Facebook that they will attend the event.

Police have imposed conditions on the march, limiting it to a three-hour period between 6pm and 9pm on a prescribed route between Trafalgar Square and Whitehall.

Any static protest must only take place in Trafalgar Square, Richmond Terrace and Parliament Square and the Met warned anyone breaching the conditions could be arrested for public order offences.

Chief Superintendent Pippa Mills said: "We will always facilitate peaceful protest and have a strong history of doing so. However we have strong reason to believe that peaceful protest is the last thing on the minds of many of the people who will come along this year.

"Criminality at the event has increased year-on-year. Last year hundreds of Londoners on their way home from work, or out enjoying an evening in the capital, were harassed and intimidated by people causing them huge concern.

"We have such serious concerns about a repetition of such criminal behaviour this year that we have made the decision to impose conditions under the Public Order Act on the event on Saturday 5 November."