Crime figures from Police Scotland "may not be consistent" with Scottish Government data and are "more selective" than figures from the previous eight forces, according to the public spending watchdog.

Audit Scotland has found "inconsistencies", "assumptions", "disagreements", "distractions" and "limited progress" in several areas of the implementation of the single police force.

While it does not focus on operational policing, it notes that police reports to governing body the Scottish Police Authority (SPA) on issues like crime and detention are now "more selective" than the old eight forces.

Audit Scotland's Police Reform report states: "Police Scotland extracts information from its performance management system to prepare performance reports at a national level for the (SPA) board and locally for reporting to councils and community planning partners.

"The Scottish Government also publishes statistical bulletins on aspects of policing, for example recorded crime and detection rates.

"Now there is a single national service, the Scottish Government is concerned that information in performance reports to the board may not be consistent with information published in its statistical bulletins.

"As a result, performance reports to the SPA board are now more selective and have less trend and comparative information than those presented previously to joint boards and police authorities."

Good data is vital to hold the chief constable to account, the report states.

There has been a 1.4% year-on-year drop in recorded crime and a 16% drop in serious crimes since the formation of the single force, according to Police Scotland figures.

An Audit Scotland spokesman said: "We are not saying that the information that they are reporting is wrong.

"We haven't audited it or validated it, but it's not a case of saying that they are presenting inaccurate information.

"But we are saying that you are now not getting that same information being reported.

"Police Scotland is reporting some of that information but not all of it, and you're also not getting it compared with previous performance.

"So, the issue that we are making is not so much about the accuracy of the information that is being reported, but more about the comprehensiveness and the clarity of it. It's about the full picture."

Audit Scotland has called for better information to support effective scrutiny of police performance.

"The SPA board needs comprehensive, reliable and transparent financial and performance information if it is to provide effective governance and scrutiny of policing and forensic services," the report states.

"The papers provided by the SPA senior management and Police Scotland for consideration by the SPA board have not always supported effective decision-making.

"For example, financial and performance information are rarely linked, there are inconsistencies in how financial information is reported and there is limited use of trend information.

"The SPA needs to know how the police service is performing to fulfil its statutory responsibility to hold the chief constable to account."

Police Scotland may have to find an additional £21 million of savings above the original business plan next year, and a further £112 million from 2016/17 to 2018/19, the report states.

Many savings are expected to come from reducing police staff costs but further savings may be challenging through the "lack of flexibility" in managing staff and officer numbers, according to Audit Scotland.

"The Scottish Government's commitment to maintain police officer numbers at 17,234 and no compulsory redundancies for police staff limits the SPA and Police Scotland's flexibility to deliver savings," the report said.

There have been difficulties in obtaining consistent data on employee numbers and attendance records, and the loss of experienced staff has further exacerbated the problem, the report states.

"The compilation of financial information is time-consuming and increases the risk of errors or fraud," the report said.

Concerns have been raised about the accuracy of financial information and the lack of a full business case for the single force despite an assurance that one would be provided by the Scottish Government.

Audit Scotland said: "The Scottish Parliament Finance Committee received an assurance from the Scottish Government that the police service was leading on developing a full business case to provide greater accuracy of the costs and savings from reform.

"The development of a full business case, based on the creation of a single police service, was not carried out."

Disputes among the police, SPA and the Scottish Government over the structure of the force, and several senior staff changes at the SPA, have caused delays and presented challenges in achieving the necessary savings.

In one example, it notes that the SPA's interim headquarters at Bremner House in Stirling has been lying empty for more than a year at an annual rental cost of £132,000.

"There have been difficult relationships between the Scottish Government, the SPA and Police Scotland throughout the reform process," the report said.

"These difficulties have resulted in considerable time being spent in meetings to resolve areas where there have been disagreements. Considerable work is now required to build mutual confidence, trust and respect."

It added: "The SPA and Police Scotland face continuing challenges and risks to delivering the savings required.

"The lack of flexibility in managing staffing levels, different financial information systems, frequent changes in senior staff and delays in developing some strategies are all contributing to the savings challenge."

Justice Secretary Kenny MacAskill said: "This report provides a snapshot of where the reform process was earlier this year. It does not reflect the considerable work which has been undertaken since then.

"However I welcome recognition that action is already being taken on many of the recommendations.

"The SPA and Police Scotland have made very good early progress. Roles and responsibilities and early release schemes have been agreed, savings are on track for the year and the development of a financial strategy is at an advanced stage.

"Good progress is also being made putting in place permanent executive level structures for the SPA and Police Scotland.

"Strong local policing and priorities are and always will be the bedrock of the service. All areas of Scotland now have equal access to specialist expertise, equipment and investigation teams.

"Better responses to local issues are being delivered through 32 local authority policing plans and 353 Ward level plans across Scotland.

"Since reform the number of elected members involved in local scrutiny arrangements has increased from 146 to 367 councillors."

The government has acknowledged the challenges of police reform and acted to resolve these issues, he added.

A Scottish Government spokeswoman added that they are working with police and the SPA to ensure that published performance information is consistent with national statistics publications "to avoid any potential for confusion or misunderstanding over different sets of published performance information".

Police Scotland deputy chief constable Neil Richardson said: "The process of change is only just beginning and while much has already been achieved there is much more to be done in partnership to deliver an efficient, modern policing service within the challenges of the financial constraints.

Police Scotland is confident of meeting its financial savings for year one, he added.

SPA chairman Vic Emery said: "The shared focus from all partners on ensuring a smooth transition allowed policing to be ready legally and organisationally for merger whilst maintaining operational services for the public.

"There is now a strong consensus on respective roles and responsibilities. The quality of information is improving in both content and presentation, and this will support SPA and Police Scotland to develop a three-year financial strategy before the end of this current financial year."

The Scottish Goverment's commitments to retain police officer numbers with no compulsory redundancies "will make achieving future savings hugely challenging", he added.

"We are confident that we will deliver all the savings required of us in this first year, and to do so with policing continuing to perform effectively for the people of Scotland."

Labour MSP Hugh Henry, convener of Holyrood's Public Audit Committee, said: "One of the main drivers for police reform was to save £1.1 billion by 2026. I am surprised to learn that no full business case was prepared to support this, nor was robust baseline information developed to measure progress. How then can the public be certain that savings are actually being made and targets met?

"I am sure that the Public Audit Committee will want to look carefully at this matter and to explore further the concerns of Audit Scotland that it is not clear how these savings will be achieved."

Labour colleague Graeme Pearson said: "This report is damning about the shambolic reorganisation which has taken place.

"We've seen a power struggle at the top which has hampered progress, but which was casually dismissed as 'creative tension' by Alex Salmond.

"With £140 million of cuts still to come, the tensions within this report will only increase. It's time for Kenny MacAskill to take responsibility for his budget cuts and show some leadership for once."

Conservative justice spokeswoman Margaret Mitchell said: "This is a damning report which reveals how egos at senior level threatened the whole process. That is a ludicrous state of affairs which should never have been allowed to happen."

Liberal Democrat justice spokeswoman Alison McInnes said: "This is extremely serious. Scottish Ministers must take action on the Audit recommendations. The Cabinet Secretary should appear before the Justice Committee to answer questions on this damning report."

Green MSP Alison Johnstone said: "It's becoming clear that this flawed centralisation of the regional forces has just created a top-heavy management that is damaging local control over services."