POLICE chiefs will need an additional £50 million over the next two years to avoid slashing officer numbers, a watchdog has said.

Stephen Boyle, an audit director at Audit Scotland, said he estimated tens of millions of pounds would be required to maintain police numbers.

It comes amid warnings that up to 750 officers will need to be cut to balance the books at Police Scotland.

Auditors also joined calls for a review into the entire police oversight structure following a “turbulent” history since the single force was created in 2013.

Mr Boyle told Holyrood’s Public Audit Committee that the Scottish Police Authority (SPA) is forecasting a deficit of £25 million in the current financial year.

He said the government is expected to cover this, as well as providing a £17 million one-off payment to allow police chiefs to shoulder costs relating to Brexit.

SNP MSP Alex Neil asked him how much additional funding the SPA would need over the next two financial years to avoid slashing officer numbers by 750.

Mr Boyle replied: “Essentially it will be tens of millions of pounds – I would assume in the region of £40-50 million that it would require in order not to have to receive continued cash allocations during the course of the next two financial years.”

He added: “That would be my assumption and estimate – that’s over the course of two financial years.

“But the specifics of it is maybe a question for SPA or Police Scotland.”

He previously told MSPs the financial situation facing the police was “undoubtedly” challenging.

He said two options had been outlined to return the force to “financial balance”.

Mr Boyle added: “One…was to reduce police numbers by 750 – a number that’s been talked about over a significant period of time – to deliver that financial balance.

“Or else the second scenario [is] to receive an uplift in funding, essentially, from government.”

Scottish Tory shadow justice secretary Liam Kerr accused the SNP of running Police Scotland into the ground.

He said: “Our police officers have been saying that they do not have sufficient funding for some time, but the SNP continues to sit on their hands.

“Under the SNP we have seen significant increases in sexual crime, violent crime and crimes of fraud which all heap increased pressure on our police service.

“The SNP cannot expect Police Scotland to function properly without enough cash so this could jeopardise public safety.

“Under the SNP our prisons are overcrowded, courts are overflowing and now police numbers could be cut by 750 – that’s a disgraceful record.”

Last year the SPA, which controls the annual £1.2bn police budget, lost its third chair since coming into being in 2013.

Professor Susan Deacon quit saying the system she oversaw was “fundamentally flawed in structure, culture and practice” and there was nothing more she could do to fix it.

She urged the Scottish Government to “think afresh” about how the police service was scrutinised and held to account.

The SPA has also been through four chief executives since its inception.

However, Nicola Sturgeon said she did not agree with Ms Deacon’s position.

During First Minister’s Questions last month, she said: “Susan Deacon is entitled to her opinion on that and I would be very happy to hear the basis on which she has reached that conclusion. However, I do not agree with that conclusion.”

Now Caroline Gardner, the Auditor General for Scotland, has also called for a review into the entire governance structure of the force, including HM Inspectorate of Constabulary in Scotland (HMICS) and the Police Investigations and Review Commissioner (Pirc).

Giving evidence to the Public Audit Committee, she said: “The recent resignation of the chair of the SPA highlights the continuing lack of clarity about how the system of policing in Scotland should operate, and the roles and responsibilities of all those involved.

“The SPA and Police Scotland were established in 2013, almost seven years ago now.

“As I reported at the time, this was a major piece of public service reform carried out very quickly, and its history since then has been turbulent.

“In my view it’s now time for a review of the way in which the system of governance and accountability as a whole is operating, taking in the roles played by the Scottish Government, HMICS and the Pirc, as well as the SPA and Police Scotland.

“In order to protect public confidence, it’s essential that everyone involved has a shared understanding of how the SPA will fulfil the role envisaged for it by the legislation, and what else is required for it to do so.”

A Scottish Government spokeswoman said: “Despite constraints on Scotland’s public services through a decade of UK austerity, we are protecting Police Scotland’s annual budget in real terms in every year of the current Parliament, and since 2016-17 the budget for policing has increased by more than £80 million, bringing it to £1.2 billion for 2019-20.

“The Scottish Crime and Justice Survey, which includes unreported crimes, shows a 46 per cent fall between 2008-09 and 2017-18 in violent incidents experienced by adults in Scotland while the proportion of adults experiencing violence fell from 4.1% to 2.3% over the decade.

“In addition, we continue to press the UK Government for a refund of the £125 million paid by Police Scotland in VAT between 2013 and 2018.”