The cost of merging Sussex and Surrey police could lead to cuts equivalent to losing more than 500 front line officers, new research has revealed.

Plans to develop neighbourhood policing would effectively be destroyed and officers could end up doing support staff jobs if the £27 million amalgamation goes ahead.

The Government expects start-up costs for IT, retirement and redundancy payments to come from forces' existing budgets, raising fears that police officers and support staff will be shed to make ends meet.

A confidential paper prepared for the Association of Chief Police Officers warned the equivalent of 25,000 officers could be cut nationally.

It says that without extra funding, the "superforces" will not be able achieve their intended goal: to improve public protection from serious crime. The report warns: "It won't even do what it says on the tin."

If Home Secretary John Reid proceeds with the reform started by his predecessor Charles Clarke, a two-county force covering 2,000 sq miles and serving more than two million people could be in place by April 1, 2008.

Nick Herbert, MP for Arundel and South Downs and shadow police minister, has calculated that the equivalent of 549 officers could be lost in Sussex.

Mr Herbert said: "This paper confirms our worst fears - that amalgamations will result in cuts to front line policing. People want to see resources invested in bobbies on the beat. They don't want money wasted on management consultants, rebranding and new offices.

"It has always been argued amalgamation would help release funds to fight serious crime, but this will do the opposite.

"A loss of more than 500 officers from Sussex Police would decimate neighbourhood policing and seriously undermine public confidence.

"The new Home Secretary should have a better sense of priorities. Police force amalgamations are a costly and unnecessary distraction."

Mr Herbert said if the money was not found by cutting officers, support staff could be targeted. He warned that officers might be forced to fill their roles, leaving them less time on the street.

He has tabled a parliamentary motion calling for a referendum before any merger goes ahead. Tory MPs have also said council tax payers could have to pay an extra £19 to bring them in line with Surrey.

The merger has been called a "marriage made in hell" by Sussex Police Authority.

Chairman Peter Jones said: "If this were to happen it would be a disaster. It would undo all the good work which has taken place over the last five years to strengthen Sussex Police."