THE NHS is "not financially sustainable in its current form" and performance against all eight key targets, including waiting times, deteriorated last year.

In her annual review of NHS Scotland, the Auditor General for Scotland Caroline Gardner said pressure is building in several areas including major workforce challenges, rising drug costs and a significant maintenance backlog.

Read more: Scottish Government waiting times improvement plan pledges to hit cancer target by 2021 

Despite achieving unprecedented savings of £449.1 million in 2017/18, she warned that health boards have relied too heavily on one-off savings to balance the books.

By the end of the current financial year, eight boards predict that they will have overspent their budget, compared to just three two years ago, and the size of the deficits are also mounting rapidly.

In 2015/16, territorial boards predicted at the start of the year they would achieve an overall surplus of £0.5 million at year-end. In 2016/17, this moved to a predicted deficit of £34.1 million. A year later, this figure almost tripled to a shortfall of £99.3m.

This has resulted in increasing amounts of brokerage - interest-free loans from the Scottish Government - being used to prop up cash-strapped boards. By the end of March this year, the total amount of outstanding loans across NHS Scotland was £102 million.

Read more: Audit Scotland says 'complex and fragmented' CAMHS system must change 

However, Health Secretary Jeane Freeman recently announced that any outstanding loans will be written-off at the end of the 2018/19 financial year.

Ms Gardner said Audit Scotland was still "carrying out further work to understand the implications of the recent announcement".

The review also warns that financial pressures will intensify over the coming decade without a substantial real terms increase in investment.

It notes that between 2008/09 and 2017/18, increases in health funding have averaged 0.8 per cent per year in real terms but that this level of increase "is unlikely to continue".

It states: "The Scottish Government five-year financial strategy, published in May 2018, sets out potential annual real terms health funding increases of between 0.24 per cent and 0.59 per cent between 2019/20 and 2022/23. At the same time, health costs are projected to increase more quickly.

"Scotland’s ageing population means that more people will be living longer with multiple long-term conditions, leading to greater costs for the NHS. Other cost pressures, such as increases in drug spending, are also projected to intensify.

"The Fraser of Allander Institute has predicted that the health resource budget is likely to have to increase by around two per cent per year in real terms to 2030 just to stand still."

Read more: Waiting times guarantee 'in tatters' after record breaches 

In the past five years alone, spending on drugs has increased 19.4% and spending on locum doctors to plug vacancies is up 40%.

Meanwhile, the review highlights an increase in patients waiting too long for operations, cancer treatment, outpatient appointments or mental health support.

No NHS boards were able to meet all eight key national waiting times targets, and NHS Lothian failed to achieve any.

Only one target - that 90% of patients referred for drug and alcohol treatment be seen within 21 days - was met, but performance against all targets had declined nationally year-on-year by the end of 2017/18.

The greatest reduction in performance nationally was seen in Children and Adolescent Mental Health Services’ (CAMHS), where just 71.2% of patients were seen within 18 weeks of referral in 2017/18, compared to 83.6% the previous year.

Cancer patients also waited longer to start treatment, and there have been substantial increases in the number of patients waiting more than 12 weeks for their first outpatient appointment - up 215% in five years.

The number waiting more than 12 weeks for an inpatient or day case procedure has also soared 544% in five years.

It comes after the Scottish Government announced a 30-month plan to drive down waiting times by 2021.

Caroline Gardner, Auditor General for Scotland, said: "The performance of the NHS continues to decline, while demands on the service from Scotland's ageing population are growing. The solutions lie in changing how healthcare is accessed and delivered, but progress is too slow."

Chair of BMA Scotland, Dr Lewis Morrison said: “One warning is repeated over and over again in Audit Scotland’s latest report: That the NHS is not in a financially sustainable position.

“This stark warning could not be any blunter, but will come as no surprise to frontline doctors who have faced the consequences of inadequate funding year after year."

Health Secretary Jeane Freeman said: "Under this Government, NHS funding has reached record levels of more than £13 billion this year, supporting substantial increases in frontline NHS staffing, as well as increases in patient satisfaction, reductions in mortality rates, falls in healthcare associated infections, and Scotland’s A&E performance has been the best across the UK for more than three years.

"While our NHS faces challenges, common with health systems across the world, we are implementing a new waiting times improvement plan to direct £850 million of investment over the next three years to deliver substantial and sustainable improvements to performance, and significantly improve the experience of patients waiting to be seen or treated.