Police at the G20 meeting in Brisbane have signalled they will take a tougher line on demonstrators than previously indicated.



The late reversal of a decision to allow protest organisers to use megaphones, as well as warnings that people carrying masks can expect to be stopped by police, sets the stage for possible arrests during otherwise peaceful demonstrations on Saturday.

Police on Friday released the details of the fourth person banned from inner Brisbane’s declared area, a former boxer with a record of violence against police.

Gavin George Begbie, who hurled a dart that lodged in an officer’s skull at the Asia Pacific Economic Cooperation forum in Sydney in 2007, is not connected with any activist group.

That follows the banning of prominent Brisbane activist Ciaron O’Reilly who planned to confront US president Barack Obama over the treatment of US army whistleblower Chelsea Manning and WikiLeaks publisher Julian Assange.



What’s the point of the G20, anyway? Find out with our animation Guardian

Under the G20 security act police are allowed to publish the details of “prohibited persons” if all attempts to contact them have been exhausted.



Both officers and protest organisers said that senior police had ruled out the use of megaphones, just days after Guardian Australia revealed their decision to permit their use to organise and rally demonstrations.



Megaphones, masks and large banners are listed in the G20 security act as “prohibited items” in the declared area – unless those carrying them have a “lawful excuse”.



Former Queensland solicitor general Walter Sofronoff told Guardian Australia this week that peaceful protest in his opinion might be a lawful excuse under the act.



But police negotiators on Thursday night informed the Brisbane community action network that decision had been changed.



Briscan was also told masks during protests were likely to be considered lawful, although those carrying them before or after demonstrations could expect to be stopped and questioned by police.



Activists said it was expected a number of demonstrators would be bringing both megaphones and masks to protests on Saturday, despite the warnings.