The following correction was printed in the Guardian's Corrections and clarifications column, Thursday 29 October 2009

In the report below on the controversy over Metropolitan police plans to make firearms officers available to commanders for duties in five London boroughs, we said these officers would carry submachine guns. The Met points out that the weapon in question is the single-shot variation of the Heckler & Koch MP5 submachine gun (the MP5SF). What we should have said, therefore, is that the officers would be carrying semi-automatics.

Metropolitan police plans for units armed with submachine guns to patrol areas of London plagued by violent drug gangs have thrown the capital's police authority into turmoil.

In a break with the traditional image of the unarmed bobby on the beat, a team of 18 constables, led by an inspector and two sergeants, will be deployed to serve as a deterrent to gangs in heavy crime areas such as Brixton and Haringey.

The officers - some on motorbikes - will be armed with Heckler & Koch MP5 submachine guns capable of firing up to 800 rounds a minute and Glock semi-automatic pistols.

The new unit will come from within CO19, the specialist firearms unit that provides armed support for their unarmed colleagues. CO19 is normally called out when there is a need for armed police, but the new unit will adopt more aggressive tactics.

"CO19 has traditionally provided a response to gun crime," said acting chief superintendent Andy Tarrant. "This new unit sees a move towards a more proactive approach to deal with weapons and people linked to violence on our streets."

The suggestion of a routine and permanent firearms presence on British streets has angered London's police authority, with members demanding to know how changes to the central philosophy of British policing could have been made without wide consultation.

On hearing of the disclosure, Catherine Crawford, the chief executive of the Metropolitan Police Authority – which is responsible for strategic issues within the Met – emailed members. "This is just to let you know that this is not a proposal on which the authority is sighted and we are making urgent enquiries of the Met," she said.

Jennette Arnold, a Labour MPA member, said: "We have spent years working on relations between the communities I represent and the police and – thanks to this hard work – they have never been better. All that hard work might as well be thrown away and the contract between the community and the police torn up if this is the future of policing in London.

"No one asked us or the people I represent if this was acceptable and when they do I shall tell them it isn't. It isn't acceptable to throw away the principle of policing by consent. I will fight this tooth and nail."

The way the Met plan has come to light will reignite the debate about who runs the police in London. Sir Paul Stephenson moved to assert his authority last month after Boris Johnson's policing adviser Kit Malthouse boasted that the mayor and his political administration had their "hands on the tiller".

At the same time, the mayor will be forced to take political responsibility unless he can show that the capital's problems with guns and gangs are being kept in check.

Gun-related crime in London has risen year-on-year with the number of gun crimes in September alone up from 230 last year to 300 this year – a 30% rise. Earlier this month it emerged that the number of so-called war wound shootings in which gang members shoot each other in the legs for "disrespecting" them more than doubled to 72 already in 2009 compared with last year.