Tony Blair has signalled a retreat over contentious plans to cut the number of police forces in England and Wales from 43 to as few as 12 next year.

The hint of compromise came as the Government prepares for anger today over new figures showing a sharp rise in street crime. It admitted yesterday that detectives were currently only able to target fewer than 100 of the estimated 1,600 major crime gangs in the country.

As the Home Office published new plans to drive up performance standards, police authority leaders lobbied Westminster to protest against the planned mergers.

Charles Clarke, the Home Secretary, last year set out proposals for England and Wales to be covered by between 12 and 23 "strategic" police forces. The four Welsh forces would be merged and several English regions could be served by a single force.

The plans have prompted opposition campaigns across the country, with police authorities refusing to co-operate.

The Prime Minister struck an emollient note yesterday, telling MPs that the plans were not set in stone. He said that existing forces could have a "strategic coming together on certain issues rather than mergers".

The Home Office announced that the amalgamations, all originally intended to take place in 2007, would be phased in over a longer period. Hazel Blears, the Home Office minister, said: "It may well be that we go in different phases in different places. There is no reason why we would have to do everything right across the country all at the same time."

However, she reminded forces resisting change that ministers had the power to impose mergers once a four-month consultation period had been completed.

The Association of Police Authorities (APA)denounced the planned changes as rushed, inflexible, costly and potentially damaging to local policing.

The APA has accused Mr Clarke of trying to "divide and rule" and of "bribing" individual forces to agree to the plans.

Under the Police and Justice Bill published yesterday, the Government will get sweeping new powers to order chief constables how to run their forces. The Home Secretary will be able to instruct a chief constable or police authority to take "specified measures". The Bill also requires airline companies operating internal flights in the UK to hand over passenger lists if police believe major criminals are on board. The power currently exists only if terrorists are thought to be on board the aircraft.

Crime figures today are expected to show the biggest rise in muggings for three years, with an annual increase of up to 40 per cent in some areas.

Mr Clarke is expected to announce a review of crime statistics by appointing an independent group of experts to investigate how they are collated.