NHS bosses have had a contract with a medical centre for almost 20 years without any formal tender arrangements being put in place to ensure value for money, a leaked report has revealed.

NHS Highland also made payments to Nairn medical centre without a signed agreement on services in place, it added.

The Tories said the report, which was commissioned by public spending watchdogs at Audit Scotland, exposed "some extremely murky goings-on at NHS Highland".

It comes after the finances of NHS Tayside have been in the spotlight, after money from public donations was used to pay for new IT systems.

The report on NHS Highland, which was obtained by the Scottish Conservatives, found that "contract monitoring is inconsistent, lacks formality and is not always documented" .

As a result of this, it said that "NHS Highland can not always demonstrate the achievement of value for money".

Audit Scotland had instructed professional services firm Grant Thornton to look at the contract with Nairn medical centre, along with another contract NHS Highland had for vasectomies, after "concerns" were identified.

The deal with NHS Highland is worth about £200,000 to Nairn medical centre but the report - produced in December 2017 - revealed this "intermediate care contract has been in place since 1998 and has not been subject to a formal tender or value for money (cost/ benefit) formal assessment".

Meanwhile, minutes of meetings between the medical centre and the health board indicated the "outcomes NHS Highland anticipated may not be being achieved".

A new agreement between the two parties reached in September 2016 included "better defined performance measures" , with NHS Highland making monthly payments to Nairn medical centre afterwards.

However, this was "not signed off by both parties until February 2017", with the report adding: "This means that NHS Highland were paying for a service which was not legally agreed by both parties."

The health board, however, said payments were being made under a pre-existing contract, although it "accepts that payments should not commence until a contract has been signed by all parties".

Grant Thornton also looked at the service level agreement NHS Highland has in place for vasectomies, noting this was for an "unusual" seven-year period.

The report further stated that as the number of procedures being carried out is increasing, the health board may want to review if the arrangement "still represents value for money".

In its response, NHS Highland agreed it was "generally accepted" the best value for contract lengths was on average four years.

Conservative Highlands and Islands MSP Edward Mountain said the report suggested that such "mismanagement could be even more widespread".

He added: "There are clearly some extremely murky goings-on at NHS Highland.

"There is no analysis of value for money, quality of care or patient satisfaction - with budgets as tight as they are, these is completely irresponsible.

"These aren't contracts for cleaning the windows, they are major deals worth hundreds of thousands of pounds of taxpayers' money concerning people's health."

An NHS Highland spokesman said: "The report is now in the public domain including our response on the matter.

"The required management actions are being taken to implement the recommendations and will be monitored via our Audit Committee."

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A Scottish Government spokesman said: "It is important that all health boards follow the relevant procurement guidelines to ensure the best use of resources.

"We have been clear that we expect NHS Highland to address the issues raised in this audit report and to fully implement its recommendations."

An Audit Scotland spokesman said: "We asked Grant Thornton, our appointed auditor for NHS Highland, to carry out an audit on specific concerns raised by others in correspondence.

"As a result, the auditor has made several recommendations. We will continue to monitor NHS Highland's response to these concerns and its wider performance as part of the annual audit process."