Elected regional police commissioners with the power to fire chief constables and a new national crimefighting agency are likely to be in place within two years, under plans to be announced by home secretary Theresa May today.

The long-trailed shake-up of police forces, which will see people vote for officials overseeing their budgets and their top officers in May 2012, has already caused protests from chief constables who have warned it could jeopardise their operational independence.

But the government insists police must be more accountable. The new National Crime Agency is expected to replace the Serious Organised Crime Agency (Soca), set up by Labour just four years ago and, like its successor, once dubbed the equivalent of the US FBI.

May, who is to publish a consultation document after addressing parliament at 3.30pm this afternoon, has already tried to reassure chief constables their independence will not be compromised after Hugh Orde, president of the Association of Chief Police Officers, warned before the election that some could quit if the changes went ahead.

Police authorities have also warned that individuals with extremist views or political agendas could seek election as commissioners.

Soca will be replaced by a new body that is expected to include a border police unit and the Child Exploitation and Online Protection Agency. It was criticised last year by the Commons home affairs select committee, which pointed to figures showing only £1 was seized from organised crime gangs for every £15 in Soca's budget. The agency recovered £78m during its first three years, but cost taxpayers £1.2bn.

A Home Office spokeswoman said: "The government wants to ensure all aspects of policing are run effectively to tackle crime.

"This includes serious and organised crime, through strong links between local policing and work done beyond individual forces."

Measures to tackle problem drinking, including stronger powers for the police and local councils to act against trouble spots and charge more for late licences to fund policing, are expected. Harsher penalties for shops selling alcohol to those underage and a ban on the sale of alcohol below cost price are also likely.